Story highlights Julian Zelizer: This has been Trump's worst week and it's shaken GOP lawmakers' wall of support for him

GOP's legislative agenda languishes as lawmakers fear Trump's actions could harm their own election prospects, Zelizer says

Julian Zelizer, a history and public affairs professor at Princeton University and a CNN political analyst, is the author of "The Fierce Urgency of Now: Lyndon Johnson, Congress, and the Battle for the Great Society." He's co-host of the "Politics & Polls" podcast. The opinions expressed in this commentary are his own.

(CNN) The news that former FBI director James Comey wrote in a memo that President Donald Trump asked him, in February, to stop investigating national security adviser Mike Flynn has sent shockwaves through Washington.

It comes amid Trump's worst week in politics, and that's saying a lot. After many months of shocking and aweing the nation, the President is finally doing something that seemed impossible -- he is threatening to crack the Republican firewall on Capitol Hill that has done more than anything else to protect him.

In general, House and Senate Republicans have stood firm as Trump has issued controversial statements and provoked international tensions. They have given him the benefit of the doubt, hoping that even though the President's first 100 days lacked any significant legislative accomplishments, the second hundred might allow the GOP to finally make progress on their agenda after eight long years in the wilderness.

Despite concerns that the health care legislation that passed the House would prove to be damaging to Senate Republicans, Senate Majority Leader Mitch McConnell said he still had confidence he could put the pieces back together into a successful initiative.

But in the span of just seven days, everything has changed. President Trump stunned the nation when he fired FBI Director James Comey in the middle of the agency's investigation into his campaign, then admitted in a TV interview that he did it because of the "Russia thing."

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