WASHINGTON — The new Democratic majority in the House confronts President Trump with a dramatically different reality on Capitol Hill and sets up the likelihood of two years marked more by conflict than cooperation.
“We won,” Representative Nancy Pelosi of California, the Democratic leader, said in an interview on Wednesday. “It is a new day in the capital of the United States. And we fully intend to take advantage of that opportunity.”
But many of the Democratic newcomers will represent the swing districts they took from Republicans. Despite the overall leftward direction of their party in recent years, House Democrats will need to be mindful of the tilt of those districts or risk losing their gains in 2020.
“The path to a majority was in moderate and right-of-center districts, so de facto the Democratic caucus will grow to the center,” said Steve Israel, a former Democratic House member from New York who previously managed the party’s campaign effort.
House Democrats must now settle quickly on their leadership, though Ms. Pelosi is increasingly confident she will become the first person since Sam Rayburn in the 1950s to lose and regain the top House job. And their victory was tempered by Republican gains in the Senate, a result that will complicate the relationship between the two chambers, especially with Senator Mitch McConnell, the Kentucky Republican and majority leader, who is emboldened by his own success.
But as Mr. Trump was celebrating his party’s success in the Senate, his experience so far has been only with a compliant Republican House and Senate, not an aggressive Democratic opposition armed with subpoena power and a wide array of investigative targets from which to choose. Both sides will be feeling their way in the coming months as they enter new territory.
Here are the factors that could define the new power-sharing arrangement between the White House and Congress.
Health care is issue No. 1.
After losing their grip on the House in 2010 in a backlash to the Affordable Care Act, Democrats were able to regain a majority by emphasizing their commitment to health insurance coverage and capitalizing on deep voter dissatisfaction with President Trump in suburban America.
The Democratic focus on health coverage for people with pre-existing conditions was a defining element of the party’s winning campaign in the House, so much so that Ms. Pelosi on Tuesday night was dissatisfied with the level of the applause she got at a victory party when she highlighted the party’s push on that issue.
“Let’s hear more for pre-existing medical conditions,” she said in a somewhat awkward rallying cry.
But the Democratic victory in the House, and the fact that Republicans were put on the defensive on the issue, means that the stalled effort to repeal the new health care law is dead for now.
Instead, Democrats intend to place a heightened emphasis on legislation that would lower the cost of prescription drugs, with a goal of getting a bill into the Senate and making Republicans take a stand on the issue. It is one area where House Democrats may align more with Mr. Trump, who has also embraced efforts to lower drug costs, than Senate Republicans.
Mr. McConnell acknowledged Wednesday that repeal was off the table, but said that continued problems with the health care law still needed to be taken on, only now on a bipartisan basis. “Rhetoric doesn’t solve the problem,” he said.
Democrats also say they intend to push other stymied legislation initiatives that could put them at odds with Senate Republicans, such as heightening background checks for gun buyers and making permanent a program that protects undocumented immigrants brought into the country as children.
Draining the swamp.
The midterm win will give House Democrats the all-important committee chairmanships that will enable them to pursue investigations of Mr. Trump and the executive branch. Democrats also plan to move rapidly on a package of campaign finance and ethics rules changes.
“Today is more than about Democrats and Republicans; it is about restoring the Constitution, checks and balances to the Trump administration,” Ms. Pelosi said late Tuesday night in a warning shot to the administration.
The president fired back early Wednesday with a warning of his own.
“If the Democrats think they are going to waste Taxpayer Money investigating us at the House level, then we will likewise be forced to consider investigating them for all of the leaks of Classified Information, and much else, at the Senate level,” Mr. Trump said in a tweet. “Two can play that game!”
The party has promised to move quickly on anti-corruption efforts that will come on top of heightened oversight of the Trump administration. Ms. Pelosi said the party would focus on “ending wealthy interests’ free rein over Washington.”
“In stark contrast to the G.O.P. Congress, a Democratic Congress will be led with transparency and openness so that the public can see what is happening and how it affects them, and that they can weigh in with the members of Congress and with the president of the United States,” she said.
Democrats may also try to obtain Mr. Trump’s tax records, setting up a showdown over access to his financial data.
Finding some common ground.
Besides the drug pricing initiative, Democrats and the White House could try to work together on a major public works bill.
Both Republicans and Democrats have called for an infusion of infrastructure spending but have disagreed on how to pay for it. Moving ahead on a big piece of road- and bridge-building legislation could pay political benefits for both sides and is probably an area where they could find consensus.
Mr. McConnell agreed Wednesday that infrastructure talks could be productive, given that areas of legislative agreement will be more limited between a Democratic House and Republican Senate.
But Mr. McConnell vowed Wednesday to continue to pursue his top objective of populating the federal courts with conservative judges, and his added numbers will make that task easier.
Winning over millennials.
Democrats attribute their success in the House to new backing from younger Americans, and they say they need to reward that group by working on issues with appeal to them.
“We ought to have an agenda that focuses on millennial voters,” said Representative John Yarmuth, a Kentucky Democrat first elected in the last Democratic takeover in 2006, mentioning college debt relief as a potential issue.
Mr. Yarmuth said Democrats must take advantage of their new power to showcase what a future Democratic government would look like.
“As opposed to when we were in the minority trying to find a message, we now have an opportunity to push an agenda that shows what we would do if we had control of the Senate and White House as well,” he said.
That push will come against an expanded Republican majority in the Senate and a president celebrating Senate victories he sees as resulting from his final campaign blitz.
The stage is set for a clash between the new House Democratic majority that will take power in January and Senate Republicans who don’t consider themselves chastened by the election results.