NEW YORK, NY - NOVEMBER 17: Retired Lt. Gen. Michael Flynn gestures as he arrives at Trump Tower, November 17, 2016 in New York City. President-elect Donald Trump and his transition team are in the process of filling cabinet and high level positions for the new administration. (Photo by Drew Angerer/Getty Images)
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NEW YORK, NY - NOVEMBER 17: Retired Lt. Gen. Michael Flynn gestures as he arrives at Trump Tower, November 17, 2016 in New York City. President-elect Donald Trump and his transition team are in the process of filling cabinet and high level positions for the new administration. (Photo by Drew Angerer/Getty Images)
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FILE - In this Feb. 1, 2017 file photo, National Security Adviser Michael Flynn speaks during the daily news briefing at the White House, in Washington. A lawyer for former national security adviser Flynn has told President Donald Trump's legal team that they are no longer communicating with them about special counsel Robert Mueller's investigation into Russian election interference, according to a person familiar with the decision who spoke to The Associated Press on condition of anonymity. (AP Photo/Carolyn Kaster, File)
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WASHINGTON, DC - JANUARY 20: Retired Army Lt. General Michael Flynn arrives for the Presidential Inauguration of Donald Trump at the US Capitol on January 20, 2017 in Washington, DC. Flynn is appointed National Security Advisor to Trump. Donald J. Trump will become the 45th president of the United States today.  (Photo by Saul Loeb - Pool/Getty Images)
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WASHINGTON, DC - JANUARY 20: Retired Army Lt. General Michael Flynn arrives for the Presidential Inauguration of Donald Trump at the US Capitol on January 20, 2017 in Washington, DC. Flynn is appointed National Security Advisor to Trump. Donald J. Trump will become the 45th president of the United States today. (Photo by Saul Loeb - Pool/Getty Images)
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Former Trump national security adviser Michael Flynn, center, arrives at federal court in Washington, Friday, Dec. 1, 2017. Court documents show Flynn, an early and vocal supporter on the campaign trail of President Donald Trump whose business dealings and foreign interactions made him a central focus of Mueller's investigation, will admit to lying about his conversations with Russia's ambassador to the United States during the transition period before Trump's inauguration. (AP Photo/Susan Walsh)
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NEW YORK, NY - NOVEMBER 29:  General Mike Flynn, Donald Trump's new national security adviser, arrives at Trump Tower on November 29, 2016 in New York City. President-elect Donald Trump and his transition team are in the process of filling cabinet and other high level positions for the new administration.  (Photo by Spencer Platt/Getty Images)
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NEW YORK, NY - NOVEMBER 29: General Mike Flynn, Donald Trump's new national security adviser, arrives at Trump Tower on November 29, 2016 in New York City. President-elect Donald Trump and his transition team are in the process of filling cabinet and other high level positions for the new administration. (Photo by Spencer Platt/Getty Images)
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Story highlights

Michael Flynn's resignation is another moment of vulnerability for the new president, whose praise for Putin's Russia has put him at odds with the GOP majority on Capitol Hill, writes Julian Zelizer

Zelizer says it could fuel investigations of the role of Russia in the election

Editor’s Note: Julian Zelizer is a professor of history and public affairs at Princeton University and a New America fellow. He is the author of “Jimmy Carter” and “The Fierce Urgency of Now: Lyndon Johnson, Congress, and the Battle for the Great Society.” He also is the co-host of the podcast “Politics & Polls.” The opinions expressed in this commentary are his own. This article has been updated with recent news developments.

(CNN) —  

Michael T. Flynn’s resignation is the second major blow to the Trump administration within the span of a week.

After the courts stopped the President’s executive order halting admission of refugees, his national security adviser is forced to step down amid revelations of his discussions with Russian officials following the election. The resignation comes in the wake of mixed signals from the White House about what would happen to Flynn.

It is not a total surprise that Flynn is the first major member of the administration to fall from power. He has always been one of the most controversial figures in Trump’s inner circle. A national security adviser whose views were seen as far outside the mainstream, Flynn bought into conspiracy theories and made anti-Islamic statements.

When he joined the chant of “lock her up” against Hillary Clinton at the Republican National Convention he made it clear that this military official had turned into a rabid partisan attack dog. Many national security experts shuddered to think that Flynn, with his outlandish views, would be the last person in the room when President Trump was making decisions about war and peace.

Now that he is gone the question is whether this turns into something bigger. The problem with Flynn was not simply his own actions but his part in a broader story that has been nagging Trump since the campaign – why is he so sympathetic to Russia and what kinds of connections have existed, if any, between his inner circle and a foreign government that aggressively intervened in the 2016 election.

Flynn’s resignation might just be the triggering event that opens the door to more investigations. Russia has been one of the few topics that has created serious rifts between the President and an otherwise loyal Republican majority on Capitol Hill. Trump’s affinity for Vladimir Putin and blind eye toward Russian aggression has been hard for many in the GOP, like Senator John McCain, to swallow.

Until now, Republicans have not done much to push back against the administration’s position but there are signs of change as some high ranking members of the GOP in the Senate have now called for an investigation.

It is also possible though that this strengthens Trump’s hand, even with today’s news from Capitol Hill. If Flynn’s departure is enough to calm some of the storms with Congress over the issue, the removal of one of the figures who has been closest to the Russians and a sign that Trump is finally hearing the anger from his congressional allies, this development might allow him to move on to different issues.

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The embarrassment over Flynn might persuade Trump, who is always concerned about winning above all else, to back away from his ongoing defense of anything that Russia seems to do and fall more in line with where the rest of his party has been on this issue. Most important, Flynn’s departure might increase the clout of other, more respected figures like Secretary of Defense James Mattis and bolster the standing of his national security team that has been off to such a shaky start.

The truth is that it can go either way – as is seemingly the case with everything that has gone down with the Trump White House. But Flynn’s departure is clearly a significant moment for this President as one of his most loyal, most controversial and most influential figures – in many ways a symbol of the angry attack style that has defined the White House – is forced to step down as a result of a scandal that has been hovering over the President, who has been in office for less than a month.

This creates a moment of vulnerability no matter how savvy Trump might be. He will now have to take steps quickly to reestablish control over his national security team and to create more confidence on Capitol Hill that someone is in charge in the Oval Office. Otherwise, Trump might find himself facing the kinds of congressional investigations that can quickly tie an administration into knots.