Democrats rode a wave of dissatisfaction with President Donald Trump to win control of the U.S. House of Representatives on Tuesday, giving them the opportunity to block Trump’s agenda and open his administration to intense scrutiny.

With a House majority, Democrats will have the power to investigate Trump’s tax returns and possible conflicts of interest, and challenge his overtures to Saudi Arabia, Russia and North Korea.

In midterm elections two years after he won the White House, Trump and his fellow Republicans expanded their majority in the U.S. Senate following a divisive campaign marked by fierce clashes over race, immigration and other cultural issues.

But Tuesday’s results were a bitter outcome for Trump after a campaign that became a referendum on his leadership.

Democrats  also could force Trump to scale back his legislative ambitions, possibly dooming his promises to fund a border wall with Mexico, pass a second major tax-cut package or carry out his hardline policies on trade.

A simple House majority would be enough to impeach Trump if evidence surfaces that he obstructed justice or that his 2016 campaign colluded with Russia. 

But Congress could not remove him from office without a conviction by a two-thirds majority in the Republican-controlled Senate.

Democrats in the House could be banking on launching an investigation using the results of U.S. Special Counsel Robert Mueller’s already 18-month-old probe of allegations of Russian interference on Trump’s behalf in the 2016 presidential election. Moscow denies meddling and Trump denies any collusion.

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U.S. President Donald Trump smiles while hosting a working lunch with African leaders during the U.N. General Assembly in New York, U.S., September 20, 2017. REUTERS/Kevin Lamarque

“Thanks to you, tomorrow will be a new day in America,” Democratic House leader Nancy Pelosi told cheering Democrats at a Washington victory party, saying House Democrats would be a check on Trump.

“The American people want peace, they want results,” Pelosi added.

Despite his party losing the House, Trump wrote on Twitter, “Tremendous success tonight.”

Democrats also captured governorships in Michigan, Illinois and Kansas. In Kansas, Republican Kris Kobach, a Trump ally who was a leader of the president’s disbanded voter fraud commission, fell to Democratic state senator Laura Kelly.

Democrats turned out in droves to register disapproval of Trump’s divisive rhetoric and policies on such issues as immigration and his travel ban targeting several Muslim-majority countries.

A record number of women ran for office this election, many of them Democrats turned off by Trump’s policy agenda.

The election results mean Democrats will resume House control in January for the first time since the 2010 election, beginning a split-power arrangement with the Republican-led Senate that may force Trump to scale back his legislative ambitions and focus on issues with bipartisan support, such as an infrastructure improvement package or protections against prescription drug price increases.

It also will test Trump’s ability to compromise, something he has shown little interest in over the last two years with Republicans controlling both chambers of Congress.