Democrats have regained control of the House — and plan to immediately take advantage of their newfound power.

The party enjoyed historic victories across the country in the 2018 midterms, unseating a string of Republican incumbents and introducing a wave of progressive first-time candidates, from Alexandria Ocasio-Cortez in New York City to Ayanna Pressley in Boston.

With those wins has also come the power to subpoena Donald Trump, launch numerous investigations into his White House administration and relaunch probes into his 2016 campaign.

On Tuesday night, as polling data was pouring in from across the country showing a Democratic takeover, New York congressman Jerry Nadler issued a warning to the president.

“This election was about accountability,” The Democrat — who is now slated to become the chair of the House Judiciary Committee — said.

“Donald Trump may not like hearing it but for the first time, his administration is going to be held accountable.

"He’s going to learn that he’s not above the law."

Elijah Cummings, another key Democrat expected to chair a House committee, warned that lawmakers “probably will” seek to demand the president’s tax returns, which he refused to disclose during the 2016 presidential elections.

Those warnings were also echoed by a source who reportedly told MSNBC’s Ari Melber the US House Ways and Means committee was intending to request Mr Trump’s tax returns if the Democrats did successfully gain control on Election Day.

Tremendous success tonight. Thank you to all! — Donald J. Trump (@realDonaldTrump) November 7, 2018

On Tuesday, Mr Nadler made clear he would be willing to use the subpoena powers his party had been handed during the crucial election.

“We’ll use subpoena power if we have to, when we have to,” he said.

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However, it remains unseen whether the Democratic Party will collectively seek to remove Mr Trump from office — an unlikely move as the US Senate remains controlled by the Republicans, who have the president to thank in part for many of the party’s narrow victories across the country.

Mr Nadler said “it’s way too early” to discuss impeachment proceedings after the midterms, while stopping just short of outright refusing to consider impeachment dependent on the outcome of a federal probe led by Special Counsel Robert Mueller.

Mr Trump has a slew of Democratic opponents to face under the new House leadership, who will now head up some of the most important congressional committees.

Maxine Waters, an ardent Trump critic who has railed against the president for refusing to disclose his tax returns, is slated to become the chair of the House Financial Services committee. Adam Schiff will now lead the US House Intelligence Committee, as Mr Cummings chairs the Oversight committee.

Each of those committees could launch major investigations into Mr Trump and his dealings, potentially leading to two years of gridlock and contentious battles between congress and the Oval Office.

On Tuesday night, Mr Nadler released a statement celebrating the Democratic victories and vowing accountability throughout Washington.

“Tonight, the American people said definitively that they want to see a government that is being held accountable to our laws, to our values, and to the interests of the American people,” he said.

“Americans are tired of watching a Republican Congress fail in its constitutional duty to hold the administration accountable for policies that rip children from the arms of their parents, that allow domestic abusers and white supremacists to get their hands on deadly firearms without a full background check, that allow voters to be intimidated and their voices suppressed, that enable pervasive corruption to influence decision making at the highest levels of government, and that undermine the rule of law and interfere with the independence of our justice system.

“This is what has been missing from the Republican congress, which has refused to uphold our laws off conduct oversight on important issues, and we must re-assert that we are a government of the people, by the people, and for the people.”