As of early Wednesday, Democrats had won 219 races and the Republicans 193, with winners undetermined in 23 races.
The Democrats flipped the Republican-held Colorado Senate, Maine Senate, Minnesota House and both chambers in New Hampshire. The final count is likely to leave Democrats with a narrow majority that could be hard to manage and preserve.
Trump's remarks on party dynamics came after Senate Majority Leader Mitch McConnell said he had spoken with House Democratic leader Nancy Pelosi about how they might "find a way forward" in a divided Congress next year.
In his victory speech, Brown said his state had provided a "blueprint for America in 2020".
"When you report fake news - which CNN does a lot - you are the enemy of the people", said Mr. Trump.
The president's party will maintain control of the executive and judicial branches of the government, in addition to the Senate, but Democrats suddenly have a foothold that gives them subpoena power to probe deep into Trump's personal and professional missteps - and his long-withheld tax returns.
Democrats have promised to hold oversight hearings on the Trump administration when they take the majority in January.
During the campaign, Pelosi urged candidates to focus on lowering health care costs and creating jobs with infrastructure investment, and she tamped down calls for impeachment.
The vote was seen as a referendum on the president, even though he is not up for re-election till 2020.
Jeff Sessions forced out as attorney general by Trump
Whitaker argued that Mueller should not be able to investigate the Trump family's finances in the course of his probe. In that scenario, Mueller's budget could be reduced "so low that his investigation grinds to nearly a halt", Mr.
The area's white and vastly rural profile outside Cincinnati is part of what is expected to keep OH from springing back easily for Democrats, Hamilton County Republican Chairman Alex Triantafilou said. The majority party in the House controls nearly all of the subpoena power and other investigative tools.
By that this strategist meant that Democrats continue to underperform among white voters, especially those without college degrees, and can not count on being able to motivate minority voters in numbers needed to turn narrow losses into narrow victories. And it doesn't even mean they weren't really important issues for many - even most - of those who voted for Trump.
The Republican side of the aisle elected mostly white men. He predicted an "invasion" from the migrant caravan making its way toward the USA and decried the "radical" agenda of speaker-in-waiting Pelosi.
He and Pelosi, the Kentucky senator said, are "not unfamiliar" with one another as longtime leaders and colleagues. In Florida, more than eight million voters cast ballots: up from six million in 2014. The polls also show Trump was a major factor: a minority of voters voted for Trump and his policies while the majority of voters displayed an anti-Trump sentiment. "And she lost. Too bad, sorry about that, Mia!"
And outside Richmond, Virginia, one-time tea party favorite Rep. Dave Brat lost to Democrat Abigail Spanberger, a former Central Intelligence Agency operative motivated to run for office after the GOP vote to gut the Affordable Care Act.
Smith and more than 100 other current House Democrats have already sent a letter to Defense Secretary James Mattis seeking a response.
Pennsylvania was particularly daunting for Republicans after court-imposed redistricting and a rash of retirements put several seats in play. "They ignored the consultants who said they should cover up their tattoos and smile more, and they ignored the powerful men of the Republican Party who never took them seriously anyway". At least three other red districts flipped to blue.
Female candidates fared particularly well in an election cycle that had been billed as the Year of the Woman. Last month, a New York Times investigation into just a handful of Trump's tax returns from the 90s revealed a complicated scheme of "outright fraud" to evade paying taxes on his father's estate. The winners included Democrat Mikie Sherrill, a former Navy pilot and federal prosecutor who ran for a suburban Newark seat.
Trump said that if the Democrats plan to "waste Taxpayer Money investigating us at the House level", then Republicans "will likewise be forced to consider investigating them for all of the leaks of Classified Information, and much else, at the Senate level".
Democrats had strong nights in both the Midwest/Rustbelt region and in the Southwest part of the USA, the regions of the country which will decide the 2020 presidential election.