As soon as Donald Trump gained the presumptive nominee title -- following his Indiana primary win Tuesday -- Democrats swiftly moved to tie the GOP standard-bearer to vulnerable Republican Senate candidates. Many had kept a distance from the billionaire businessman even as they acknowledged they would eventually support whoever wins the GOP nomination.
"This is no longer a drill," said a series of press releases from the Democratic Senatorial Campaign Committee in Washington aimed at eight Republican senate candidates that argued GOP inaction on Judge Merrick Garland's nomination to the Supreme Court meant the unpredictable Trump could be the one to fill that vacancy.
One of those targeted was Sen. Kelly Ayotte New Hampshire who is in a tight re-election battle against the Democratic governor of that swing state, Maggie Hassan.
"Ayotte would let the man who wants to ban Muslims from entering the country, called Mexican immigrants 'rapists' and said women should be punished for having an abortion nominate someone to a lifetime appointment to the Supreme Court," the DSCC statement said.
Moments after Trump won Tuesday -- and his chief opponent Sen. Ted Cruz of Texas dropped out of the GOP primary race -- Hassan issued a statement calling on Ayotte "to make her support for Trump official" because they "clearly are in agreement" on many key issues.
Liz Johnson, a spokeswoman for the Ayotte, told the New Hampshire Union Leader
that the senator would support Trump but not officially endorse him, the distinction between the two not being clear.
"As she's said from the beginning, Kelly plans to support the nominee. As a candidate herself, she hasn't and isn't planning to endorse anyone this cycle," Johnson said. Johnson did not respond to a request for clarification from CNN.
Ayotte is one of five GOP senate candidates considered vulnerable, in part, because they are running in states President Barack Obama won in 2012 and 2008. If Democrats can win four of those seats, they will win back control of the Senate, which they lost two years ago. Making matters even tougher for Republicans is that they have to defend 24 seats -- as many as 12 of which Democrats consider possible takeovers -- while Democrats have to protect just 10, most of which are considered safe.
The National Republican Senatorial Committee said the Trump attacks are a sign that Democrats aren't laying out their vision for the future, and also said Democratic front-runner Hillary Clinton could pose a similar problem.
"There is a reason Democrats aren't lining up to campaign with Hillary Clinton," NRSC spokeswoman Alleigh Marre said in a statement. "She is a toxic candidate whose failed leadership has put the security of our country at risk."
Both parties believe control of the Senate over the next two years is crucial. Republicans see it as a firewall against the liberal policies and nominees of Hillary Clinton if she wins the White House and Democrats see it as a critical defense against the uncertain actions of Trump if he wins.
One of those endangered Republicans, Rob Portman of Ohio, has said for months he would support whoever is the GOP nominee. A spokesman for his Democratic opponent, former Ohio Gov. Ted Strickland, described Trump's rise as Portman's "election nightmare."
"Trump at the top of the ticket will alienate the independent voters who decide elections in Ohio -- while turning off moderate Republicans and energizing Democrats across the state. With the Republican National Convention in Cleveland, there will be no rock that Portman can hide under to avoid his Party's toxic nominee," said the statement from David Bergstein.
Portman had backed Gov. John Kasich's bid for the GOP presidential nomination, who ended his campaign Wednesday. In a statement Portman praised Kasich but remained silent on Trump.
Complicating matters for Portman further is word that Trump is considering Portman as a vice presidential pick, a campaign source told CNN. But Portman's spokesman Kevin Smith said he wasn't interested and was focused on his Senate re-election.
The Pennsylvania Democratic Party targeted Republican Sen. Pat Toomey, who is seeking his second term in what is expected to be a close race against Democrat Katie McGinty, with a series of questions aimed to tying Toomey to Trump.
"Does Toomey think Donald Trump is qualified to nominate the next Supreme Court justice?" the statement asked. "How does Toomey square his support of Trump with the presidential nominee's belief that 'wages are too high' in America?"
Toomey initially endorsed Sen. Marco Rubio, R-Florida, for president. After Rubio dropped out, Toomey voted for Cruz in the Pennsylvania primary. But like so many Republican elected officials, even those wary of Trump, he has said he will also back whoever wins the nomination.
In other races, Sen. John McCain's Democratic opponent argued in a fundraising appeal that the Arizona Republican is "more vulnerable than ever" with Trump at the top of the ticket.
"Donate $5 to defeat John McCain," Rep. Ann Kirkpatrick wrote supporters of her campaign, which polls show is doing surprisingly well against McCain, who is seeking his sixth term.
McCain, a former GOP presidential nominee himself, has repeatedly said he has concerns about many of Trump's policies but would nevertheless support him if he wins the GOP nod. But he told CNN he planned to skip the convention in Cleveland. A former longtime senior aide to McCain, Mark Salter, announced this week he would vote for Democratic presidential candidate Hillary Clinton over Trump.
In Illinois, where Sen. Mark Kirk is considered one of the most endangered Republicans running, his Democratic opponent, Rep. Tammy Duckworth, highlighted an interview Kirk did with a local TV station in which he appears to say he would support Trump if he were the nominee.
"A Trump presidency is unthinkable to most Illinois voters, but not Mark Kirk," a Duckworth campaign spokesman said.
Kirk's office did not respond to a request for comment.
One vulnerable Republican is not keeping distance from Trump. Ron Johnson of Wisconsin, who is being challenged by Russ Feingold, a liberal former Democratic senator, told CNN's Manu Raju in late March that he would "stump with Trump,"
even though the first term senator has not formally endorsed him.
"Certainly as I travel the state extensively I hear a lot of support because what Donald Trump is saying resonates with an awful lot of people when it comes to the incompetence of Washington D.C.," Johnson said.