Editor’s Note: Julian Zelizer is a professor of history and public affairs at Princeton University and author of “The Fierce Urgency of Now: Lyndon Johnson, Congress, and the Battle for the Great Society.” The opinions expressed in this commentary are his own. View more opinion at CNN.

CNN  — 

Court filings on Friday regarding Paul Manafort and Michael Cohen reveal the ways in which the special counsel’s investigation can endanger President Trump’s future. Special Counsel Robert Mueller also revealed on Tuesday that former national security adviser Michael Flynn offered “substantial assistance” to the Russia investigation – the same day Maryland and the District of Columbia issued subpoenas in their emoluments case against President Trump.

Julian Zelizer

Trump, concerned that the other shoe will finally drop when Mueller delivers his final report, unleashed a blitz of tweets early Friday attacking the investigation. Trump tried to discredit Mueller and tweeted, “We will be doing a major Counter Report to the Mueller Report. This should never again be allowed to happen to a future President of the United States!” While the tweets are the words of an angry man, they also appear to be the words of a worried man.

Amid the turmoil, Trump announced major personnel changes in his administration. The President said he will nominate State Department spokeswoman Heather Nauert as UN ambassador and William Barr as attorney general. Meanwhile, Chief of Staff John Kelly is expected to step down soon.

The cynic rightly responds to all of this week’s news by asking – who cares? We have seen this kind of chaos before.

The theory is that partisanship will save this President. After all, Republicans will still control the Senate in 2019 with an even larger majority, so the likelihood of their support in any impeachment proceedings is slim. Republicans have stood by silently as the President ignores norms, threatens institutions, and conducts his erratic term in office. When it comes to taking a stand, congressional Republicans have done nothing to demonstrate that they privilege governance over partisanship.

But do the past two years suggest President Trump is immune to the fallout that could result from the emoluments case or a damning Mueller report?

In short, the answer is no. The same intense partisanship within the Republican Party that has protected President Trump until this point could just as easily turn against him. That is the essence of intense partisanship. Decisions are not about loyalty to an individual or principle but about power. When a person stands in the way of power, then they become disposable.

Until the midterm elections, Republicans were feeling pretty good. They controlled the White House and the Congress, and with Justice Brett Kavanaugh’s confirmation, the Supreme Court now leans considerably to the right as well. Republicans also amassed control of a huge number of state legislatures and governorships under President Obama. Combined with the political propaganda machine called Fox News, the party was feeling pretty good about themselves.

Even if President Trump made members of the GOP cringe and went against certain political principles like free trade, it was still unclear how things would play out at the polls. While Republicans could not ignore the dismal approval ratings of the President, factors like redistricting, along with favorable Senate election prospects and voting restrictions, could have mitigated a blue wave.

But that’s not what happened. The midterm elections served a devastating blow to the GOP. Republicans lost the House and a significant number of state-level elections in the process. While Republicans in states like Wisconsin and Michigan are trying to limit the powers of incoming governors and other officials, Democrats will still have power. Democrats even showed that they are gaining strength in places like Arizona and Texas.

Meanwhile, the stock market has plunged this week, undercutting the GOP’s confidence in the policies of “Tariff Man,” who until now had been enjoying the kind of economic rewards that kept skeptics quiet.

What happens when Republicans learn what Robert Mueller has uncovered? What if the report produces clear and compelling evidence that the President and his associates committed high crimes and misdemeanors? What if the emoluments case shows that the President, through his hotel, has exchanged political decisions for bulk hotel reservations? What if the Congress learns that everything people suspected is just the tip of the iceberg?

The thing about scandals is that they can take on a life of their own. While Republicans have tried to stifle the investigation thus far, that can change once the facts are out there. The details will matter. If the findings are damaging enough, the report can leave a lasting impact by forcing Republicans to think twice about standing by the President through 2020.

In many scandals – even Watergate – the party of the accused remained loyal to the alleged wrongdoer for a long time until the political costs become very clear.

If the House moved forward and voted for articles of impeachment, the biggest question has to do with the Senate, where two-thirds of the chamber would have to vote in favor of removing a president. Will there be enough evidence to persuade 20 Republicans to join Democrats in favor of a conviction?

Ironically, the other insurance policy that President Trump has been counting on – the very conservative Vice President Mike Pence – can turn into a liability. After all, if Republicans reach a tipping point in 2019 and determine that a scandal-ridden President can drag down the rest of the party, they might rally behind Pence for president, assured that he would stay loyal to the party agenda.

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    These are unsettling days for the Trump administration. The President is hoping that he can simply ignore what the investigators have to say or else just tweet them out of existence. But that’s not how Washington works. It is a tough town and there are breaking points for any party when the costs of supporting a politician become unbearable. That’s when the partisanship that the President has counted on could turn into his biggest problem.