President Donald Trump was the biggest name not on the ballot for elections Tuesday night, but he still lost — and won — in a number of significant ways.

Nowhere was that clearer in the split result that was on track to expand U.S. Senate control by Trump's fellow Republicans, while flipping control of the House of Representatives to Democrats.

Both outcomes will likely have major effects, positive and negative, on Trump's agenda — and possibly the fate of his presidency.

But the president also Wednesday could see political downside for him in the results from state-level elections. On the other hand, GOP victories in key presidential swing states could bolster Trump's confidence of winning re-election in 2020.

Here's how Tuesday's mixed midterm results could affect Trump.

The House

No result is more damaging for Trump and his agenda than Democrats regaining control of the House.

It puts staunch Trump foe Rep. Nancy Pelosi, D-Calif., on track to return as speaker.

The Democratic victory means the party has effective veto power over legislative initiatives sought by the Trump administration.

To get a bill passed into law, Trump, and Republicans in the Senate and the House, will have to negotiate with Democrats in ways they have not been accustomed to for some time.

In particular, Republicans will be unable, as they tried to do in 2017, to effectively repeal and replace much of the Affordable Care Act, as the Democrat-backed Obamacare law is formally known.

With their regained power, Democrats, who will take over committee chairships, also will be in position to investigate Trump and his administration in a variety of areas that Republicans showed scant interest in examining when they controlled the House.

That includes eyeing the president's campaign contacts with Russians, foreign financial connections to the Trump Organization, Trump's immigration enforcement actions and controversial spending by a number of Cabinet secretaries.

Rep. Jerrold Nadler, D-N.Y., who will become chairman of the Judiciary Committee, pointedly reminded Trump on Tuesday night that "he and his administration will be held accountable."

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Another big target for Democrats in the House will be Trump's personal income tax returns, which the president, flying in the face of decades of common practice by his predecessors, has refused to make public.

MSNBC reported Tuesday night that Democrats in control of the House Ways and Means Committee plan on requesting Trump's tax returns under a federal law that gives them such power. Sources who spoke with MSNBC said the committee will be willing to go to court to force Trump to comply with a subpoena for his returns if he refuses.

Asked at a news conference Wednesday what he would do if a subpoena is issued for his tax returns, Trump said, "Look, they're under audit, they're extremely complex, people wouldn't understand them."

"People don't understand tax returns," he said. Trump added that he would consider releasing his returns once an audit was completed by the IRS, but "nobody turns over returns when it's under audit."

Trump also warned that if House Democrats inundate his administration with subpoenas, "we're going to do the same thing," and predicted the government would then effectively shut down.

House Democrats now also will have the power to impeach Trump if they choose.

But Pelosi has dumped cold water on that idea, which has been pushed by some Democrats, telling PBS' "News Hour" "that's not what our caucus is about."

The Senate

The fact that Republicans not only retained their majority in the Senate, but will add several seats, was Trump's biggest victory Tuesday night.

That win means Trump will be able to continue nominating, and winning approval for those nominations, of conservatives to the federal judiciary.

While the Senate's recent controversial approval of federal appellate Judge Brett Kavanaugh to the Supreme Court received widespread attention, Trump in his first two years had also won approval from the Senate for 83 other nominees to the federal bench.