Some Democrats have also called for starting impeachment hearings against Trump, but mostly appear willing to wait to see what information Mueller produces from his 18-month investigation.
House Democratic leader Nancy Pelosi is hailing "a new day in America".
Two issues more than any others were on voters' minds. Some 25% described health care and immigration as the most important issues in the election.
The political and practical stakes were sky-high.
Democrats needed a net gain of 23 seats to control the House and gain a check on President Donald Trump. As this was the region that was seen as one which gave Trump the presidency, the deep rejection of the GOP there has to be seen as a unsafe development for the president.
Later, though, he acknowledged the audit would not prevent the release of his tax returns.
Trump's personal income taxes, which he withheld during the 2016 campaign and in his two years in office, are expected to be the purview of the House Ways and Means Committee.More news: Could Steelers use franchise tag on Le'Veon Bell again?
The law Democrats would use to demand the tax returns was created during the Teapot Dome scandal in the Harding administration, when lawmakers were investigating conflicts of interest during the White House at that time.
An expanded majority in the Senate will allow Republicans to continue confirming Trump's nominees to key posts.
They argue that such favours to Trump include Chinese government trademarks for his companies, payments for hotel room stays and event-space rentals by representatives of Saudi Arabia and Kuwait, and proceeds from Chinese or Emirati-linked government purchases of office space in Trump Tower.
The November 6 midterm election was a very good one for the Democrats.
Tlaib, 42, became the first Muslim woman elected to the Michigan Legislature in 2008.
He bet big on a xenophobic closing message, warning of an immigrant "invasion" that promised to spread violent crime and drugs across the nation. President Barack Obama's Democrats lost 63 seats in 2010. That didn't matter. All of them won re-election. They included New Jersey Sen Cory Booker, California Sen Kamala Harris, former New York City mayor Michael Bloomberg and former Vice President Joe Biden.
Democrats' performance in the House battlefield was mixed. The Republican incumbent had been branded Barbara "Trumpstock" by Democrats in a race that pointed to Trump's unpopularity among college-educated women in the suburbs.
Democrat Abigail Spanberger of Virginia defeated Republican incumbent Dave Brat in suburban Richmond to put Democrats over the top. Some 35 Senate seats were in play, as were nearly 40 governorships and the balance of power in virtually every state legislature. Bernie Sanders of Vermont, Elizabeth Warren of Massachusetts, Sherrod Brown of Ohio, Sen.More news: Billboard names Ariana Grande 2018 Woman of the Year
New York Democratic Governor Andrew Cuomo - sometimes spoken of as a 2020 presidential contender - cruised to a third term.
For Trump, the evening unfolded at a watch party in the White House residence, where the East Room and the State Dining Room were set up with large-screen TVs.
History was working against the president in both the House and the Senate.
Tuesday's elections also tested the strength of a Trump-era political realignment defined by evolving divisions among voters by race, gender, and especially education. In Maine, voters elected Democratic gubernatorial candidate Janet Mills after the outgoing Republican Gov. Paul LePage blocked a legislatively approved expansion for a year.
In suburban areas where key House races were decided, female voters skewed significantly toward Democrats by a almost 10-point margin.
That's a big part of the story of 2018: many demographic groups swinging far more Democratic than they did in 2014, a wave year for Republicans. All are Democrats. While Republicans also had some firsts - first female governor of South Dakota, first female senator from Tennessee - the Democratic wins showed a party that is embracing diversity, in stark contrast to the GOP.
History was also made in New England, where two states elected their first African-American congresswomen: Ayanna Pressley in MA and Jahana Hayes in CT.More news: Sri Lanka House Speaker Says Rajapaksa Must Prove Majority
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