CNN Illustration/Getty Images
Now playing
03:54
Mueller is on the Trump money trail
Retired Lt. Gen. Michael Flynn arrives at the Trump Tower for meetings with US President-elect Donald Trump, in New York on November 17, 2016. / AFP / Eduardo Munoz Alvarez
EDUARDO MUNOZ ALVAREZ/AFP/Getty Images
Retired Lt. Gen. Michael Flynn arrives at the Trump Tower for meetings with US President-elect Donald Trump, in New York on November 17, 2016. / AFP / Eduardo Munoz Alvarez
Now playing
02:49
Sources: Flynn worried about son's legal fate
WASHINGTON, DC - FEBRUARY 14:  White House senior policy adviser Stephen Miller waits for the beginning of  a parent-teacher conference listening session at the Roosevelt Room of the White House February 14, 2017 in Washington, DC. Alex Wong/Getty Images)
Alex Wong/Getty Images
WASHINGTON, DC - FEBRUARY 14: White House senior policy adviser Stephen Miller waits for the beginning of a parent-teacher conference listening session at the Roosevelt Room of the White House February 14, 2017 in Washington, DC. Alex Wong/Getty Images)
Now playing
00:55
Mueller interviews top WH aide Stephen Miller
Getty Images/CNN
Now playing
02:05
Poll: Americans concerned about Russia probe
Robert Mueller senate protection bill ath_00000000.jpg
Robert Mueller senate protection bill ath_00000000.jpg
Now playing
00:45
Senator: Mueller bill sends a message to Trump
NEW YORK, NY - AUGUST 08:  Robert S. Mueller III, Director of the Federal Bureau of Investigation (FBI), speaks at the International Conference on Cyber Security (ICCS) on August 8, 2013 in New York City. The ICCS, which is co-hosted by Fordham University and the FBI, is held every 18 months; more than 25 countries are represented at this year's conference.  (Photo by Andrew Burton/Getty Images)

CLEVELAND, OH - JULY 21:  Republican presidential candidate Donald Trump gives two thumbs up to the crowd during the evening session on the fourth day of the Republican National Convention on July 21, 2016 at the Quicken Loans Arena in Cleveland, Ohio. Republican presidential candidate Donald Trump received the number of votes needed to secure the party's nomination. An estimated 50,000 people are expected in Cleveland, including hundreds of protesters and members of the media. The four-day Republican National Convention kicked off on July 18.  (Photo by Chip Somodevilla/Getty Images)
Getty Images
NEW YORK, NY - AUGUST 08: Robert S. Mueller III, Director of the Federal Bureau of Investigation (FBI), speaks at the International Conference on Cyber Security (ICCS) on August 8, 2013 in New York City. The ICCS, which is co-hosted by Fordham University and the FBI, is held every 18 months; more than 25 countries are represented at this year's conference. (Photo by Andrew Burton/Getty Images) CLEVELAND, OH - JULY 21: Republican presidential candidate Donald Trump gives two thumbs up to the crowd during the evening session on the fourth day of the Republican National Convention on July 21, 2016 at the Quicken Loans Arena in Cleveland, Ohio. Republican presidential candidate Donald Trump received the number of votes needed to secure the party's nomination. An estimated 50,000 people are expected in Cleveland, including hundreds of protesters and members of the media. The four-day Republican National Convention kicked off on July 18. (Photo by Chip Somodevilla/Getty Images)
Now playing
02:34
Can Trump fire Mueller?
Former FBI Director Robert Mueller, special counsel on the Russian investigation, leaves the US Capitol building following a meeting with members of the US Senate Judiciary Committee on June 21, 2017.
SAUL LOEB/AFP/Getty Images
Former FBI Director Robert Mueller, special counsel on the Russian investigation, leaves the US Capitol building following a meeting with members of the US Senate Judiciary Committee on June 21, 2017.
Now playing
02:56
Mueller to WH: Preserve Trump Jr. meeting docs
Former FBI Director Robert Mueller has been appointed by the Justice Department as a special counsel to over see an investigation in Russian influence in the 2016 elections. In this photo Mueller testifies before the Senate Judiciary Committee in 2011 in Washington, DC.
Win McNamee/Getty Images
Former FBI Director Robert Mueller has been appointed by the Justice Department as a special counsel to over see an investigation in Russian influence in the 2016 elections. In this photo Mueller testifies before the Senate Judiciary Committee in 2011 in Washington, DC.
Now playing
01:07
The man who led the Russia investigation
Watson/Getty Images/Lovetsky/AP
Now playing
01:27
Things Trump has said about Putin
SAUL LOEB/AFP/Getty Images
Now playing
02:15
12 times Trump, aides denied Russian collusion
FBI Director nominee Christopher Wray testifies on Capitol Hill in Washington, Wednesday, July 12, 2017, at his confirmation hearing before the Senate Judiciary Committee. (AP Photo/Pablo Martinez Monsivais)
Pablo Martinez Monsivais/AP
FBI Director nominee Christopher Wray testifies on Capitol Hill in Washington, Wednesday, July 12, 2017, at his confirmation hearing before the Senate Judiciary Committee. (AP Photo/Pablo Martinez Monsivais)
Now playing
00:59
Mueller not on witch hunt, says FBI nominee
clapper aspen
CNN
clapper aspen
Now playing
02:06
Clapper: Officials should act if Mueller fired
Trump day Twitter orig vstan dlewis_00000000.jpg
CNN Photo Illustraton/Getty Images
Trump day Twitter orig vstan dlewis_00000000.jpg
Now playing
02:27
Trump won't stop tweeting amid Russia probe
Trump confirm obstruction investigation jones nr_00002505.jpg
Twitter
Trump confirm obstruction investigation jones nr_00002505.jpg
Now playing
02:17
Trump says he's being investigated over Comey
Jared Kushner, son-in-law and senior aide to US President Donald Trump, looks on before a meeting of the House and Senate leadership with Trump in the Roosevelt Room at the White House in Washington, DC, on June 6, 2017. (NICHOLAS KAMM/AFP/Getty Images)
NICHOLAS KAMM/AFP/Getty Images
Jared Kushner, son-in-law and senior aide to US President Donald Trump, looks on before a meeting of the House and Senate leadership with Trump in the Roosevelt Room at the White House in Washington, DC, on June 6, 2017. (NICHOLAS KAMM/AFP/Getty Images)
Now playing
01:31
Report: Mueller examining Kushner's finances

Story highlights

Sources described an investigation that has widened to focus on possible financial crimes

The increased financial focus hasn't gone unnoticed by President Donald Trump

(CNN) —  

Federal investigators exploring whether Donald Trump’s campaign colluded with Russian spies have seized on Trump and his associates’ financial ties to Russia as one of the most fertile avenues for moving their probe forward, according to people familiar with the investigation.

The web of financial ties could offer a more concrete path toward potential prosecution than the broader and murkier questions of collusion in the 2016 campaign, these sources said.

One year after the FBI opened an investigation, the probe is now managed by special counsel Robert Mueller. Sources described an investigation that has widened to focus on possible financial crimes, some unconnected to the 2016 elections, alongside the ongoing scrutiny of possible illegal coordination with Russian spy agencies and alleged attempts by President Donald Trump and others to obstruct the FBI investigation. Even investigative leads that have nothing to do with Russia but involve Trump associates are being referred to the special counsel to encourage subjects of the investigation to cooperate, according to two law enforcement sources.

The increased financial focus hasn’t gone unnoticed by Trump, who warned Mueller, via an interview with The New York Times, that his financial dealings were a red line that investigators shouldn’t cross. But the order establishing the special counsel makes clear Mueller is authorized to investigate any matters that “arose or may arise directly from the investigation.”

In response to this CNN story, the President’s attorney, Jay Sekulow, said, “President’s outside counsel has not received any requests for documentation or information about this. Any inquiry from the special counsel that goes beyond the mandate specified in the appointment we would object to.”

In 2015, the FBI began investigating cyber breaches targeting US political organizations, including the Democratic National Committee.

In the summer of 2016, US intelligence agencies noticed a spate of curious contacts between Trump campaign associates and suspected Russian intelligence, according to current and former US officials briefed on the investigation. James Comey, in his Senate testimony, said the FBI opened an investigation into Trump campaign-Russia connections in July 2016. The strands of the two investigations began to merge.

In the months that followed, investigators turned up intercepted communications appearing to show efforts by Russian operatives to coordinate with Trump associates on damaging Hillary Clinton’s election prospects, officials said. CNN has learned those communications included references to campaign chairman Paul Manafort.

A year later, the FBI is reviewing financial records related to the Trump Organization, as well as Trump, his family members, including Donald Trump Jr., and campaign associates. They’ve combed through the list of shell companies and buyers of Trump-branded real estate properties and scrutinized the roster of tenants at Trump Tower reaching back more than a half-dozen years. They’ve looked at the backgrounds of Russian business associates connected to Trump surrounding the 2013 Miss Universe pageant. CNN could not determine whether the review has included his tax returns.

In recent weeks, investigators have also started looking into the June 2016 meeting in Trump Tower and how the White House responded to news of that meeting. The session included Trump Jr., Manafort, Trump’s senior adviser and son-in-law Jared Kushner, and a Russian attorney.

Trump has denied any collusion and maintains that his business empire has “no involvement with Russia” and that he has “no loans, no nothing” from Russia. His lawyers have detailed a few exceptions, including the Miss Universe pageant he held in Moscow and the Florida mansion he sold to a Russian oligarch in 2008. Trump earned more than $100 million from those deals, according to his lawyers.

“This is like any investigation,” says one person briefed on the probe. “You start at the core and then move to the periphery. You have to explore the finances. Where this is going is no different from any investigation.”