Story highlights Julian Zelizer: For Trump, Ryan and the GOP, the stakes are enormous

Julian Zelizer, a history and public affairs professor at Princeton University and a New America fellow, 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) This week's vote on the health care plan will be a key moment in the political history of the Trump presidency. A huge amount of political capital, for everyone involved, rests on the outcome of the vote in the House. The final decision will also have massive policy implications for the President and both parties on Capitol Hill.

While President Trump has accomplished a lot in his first 100 days when it comes to deregulating the economy through executive action and challenging the legitimacy of government institutions -- part of Steve Bannon's mission to "deconstruct the administrative state" -- the legislative front has just sounded like crickets. President Trump has been incredibly ineffective when it comes to moving bills through the House and Senate. Most of the marquee items from the campaign have stalled.

This is his first real test, and it's a doozy. Repealing the Affordable Care Act has been a centerpiece of Republican politics since the legislation first passed. From day one Republicans have been aiming their political guns at this bill, promising to get rid of it one way or another.

The legislation has become a symbol for his foes of everything that they believed was wrong with President Obama. The extreme rhetoric that the GOP has used to describe this program has painted the policy as the source of all that is bad in health care. During his campaign, Donald Trump was a fierce opponent of ACA and promised to get rid of "Obamacare" if he won.

Well he did and now is his chance. President Trump has thrown his support behind the plan put forward by Speaker Paul Ryan, which would eliminate much of ACA (keeping a few parts, such as allowing people under 26 to stay under their parent's coverage and the ban on discriminating against people with pre-existing coverage) and replacing it with a system of tax credits that will allow Americans to write off the costs of their insurance.

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