Act III of the Trump presidency, which can often feel like an off-Broadway production, officially begins at noon Thursday when Democrats take control of the House and everything changes for Donald Trump.

Republicans controlled the House for the first two years, or acts, of the “Trump Show,” but their oversight was conducted with a light touch. And they never hit a breaking point with Trump and his unique approach to and views about the presidency.

But the opposite is true of returning and freshman Democrats as they take control of the House chamber. They long ago became fed up with the 45th president’s reality show-like style, from his far-right immigration policies and rhetoric to his willingness to insult political foes on a daily basis to his use of Twitter to his disparaging longtime U.S. allies and apparent affection for strongmen like Russia’s Vladimir Putin, China’s Xi Jinping and Turkey’s Recep Erdoğan.

“It’s a new political world for the president. Get ready for a new day,” Senate Minority Whip Richard J. Durbin said Thursday.

[Trump Digs In For Border Wall Fight With Foe His Base Loves to Hate]

The veteran senator predicted “more balance” in “decision-making in Washington” when the clock strikes noon. “That’s not something the president has invited,” the Illinois Democrat told CNN.

Watch: How does impeachment work?

Here are three things to watch as House Democrats and Trump prepare to do battle for two years.

Donald vs. Nancy

The president has done little to build even a working relationship with the incoming speaker, but reportedly respects her as a strong leader of her party whom he sees as a formidable foe.

She has said she is willing to work with him on common goals like infrastructure and lowering drug prices. But Pelosi has not shied away from criticizing the president in public. Wednesday, after a meeting at the White House that failed to produce a border security spending deal, was one of those times.

“We’re asking the president to open up government,” she told reporters, referring to her plan to bring to the floor a spending package featuring bills passed by the GOP-run Senate. “We are giving him a Republican path to do that.” Then her voice grew more exasperated as she added: “Why would he not do it? Why would he not do it?”

And during a televised Dec. 11 Oval Office meeting, she snapped this at Trump: “Please don’t characterize the strength that I bring to this meeting as the leader of the House Democrats, who just won a big victory.”

Both are political fighters. Both are counter-punchers. Fireworks are inevitable.

‘Exciting’ 2019?

That’s how Trump, during defensive and meandering remarks Wednesday during a Cabinet meeting, described how he sees 2019 playing out.

“It’s going to be a very exciting year. I think it’s going to be a very good year,” the president said before acknowledging his new reality.

“Some people think it’ll be controversial and tough, and it probably will,” he said as several Democratic-controlled House committees ramp up to investigate many aspects of his presidency and 2016 campaign. “But we’re going to get a lot done. I think we can work with the Democrats, actually, and get quite a bit done.”

However, rather than rattling off a list of potential issues on which the two parties might collaborate, he could come up with only one.

“We’re looking at infrastructure, we’re looking at many things that can happen,” he said before looking backward: “We just did a very big and very highly touted criminal justice reform bill, and that’s a very bipartisan thing and we finished off the year with that.”

[Trump Compares His Win, Romney’s Loss in Responding to Harsh Critique]

But a partial government shutdown Trump triggered by rejecting a Senate stopgap spending measure he previously signaled he would sign only delays work on an infrastructure bill. And on Thursday morning, he again accused Democrats of approaching the shutdown through a lens of “strictly politics!”

“The Shutdown is only because of the 2020 Presidential Election. The Democrats know they can’t win based on all of the achievements of ‘Trump,’ so they are going all out on the desperately needed Wall and Border Security — and Presidential Harassment,” he tweeted.

Mueller watch

The new year, however, could prove “exciting” for another reason. As special counsel Robert S. Mueller III continues his 2016 Russia election meddling investigation — and federal and state prosecutors in New York continue their probes of Trump’s businesses and associates — Pelosi and House Democrats will be under intense pressure from their progressive wing to begin impeachment proceedings.

Impeachment will be a political decision that Pelosi could have to make. But indictment would be up to Mueller and likely Trump’s hand-picked attorney general nominee, William Barr.

Legal scholars are split on whether a sitting president could be indicted, but in comments that will add even more spice to their relationship once Pelosi takes the gavel Thursday afternoon, she refused to rule it out.

“I do not think that that is conclusive. No, I do not,” she told NBC News. “I think that that is an open discussion. I think that is an open discussion in terms of the law.”