(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.Julian Zelizer: This has been Trump's worst week and it's shaken GOP lawmakers' wall of support for himGOP's legislative agenda languishes as lawmakers fear Trump's actions could harm their own election prospects, Zelizer says
For all the talk about populism and his maverick appeal, the heart and soul of _'s survival has been the power of partisanship.