Republicans cemented control of the Senate for two more years Tuesday and positioned themselves for a more conservative majority, with victories by candidates who aligned closely with President Trump.
North Dakota Representative Kevin Cramer and Indiana businessman Mike Braun, both staunch Trump allies, won seats held by Democrats. Representative Marsha Blackburn, a Republican and another Trump loyalist, defeated a popular former governor in Tennessee.
The results held implications for coming battles over the federal judiciary, trade, health care, government spending, and immigration. Trump’s worldview is expected to be reflected strongly in those debates in the wake of Tuesday’s elections.
The outcomes also held significance for Trump himself. His administration could face an onslaught of investigations beginning next year, as Democrats closed in on a takeover in the House. Some Democrats have even raised the possibility of impeachment.
With the map in their favor, Republicans — who currently control both chambers of Congress — were on track to preserve and expand their 51-49 advantage in the Senate. Analysts across the political spectrum had favored them to remain in power, even as they said Democrats were likely to wrest control of the House.
‘‘I see two things,’’ said Jim Manley, a former top Democratic Senate aide, looking ahead. ‘‘A president unwilling to tone down his rhetoric, along with the Senate Republicans unwilling to break with him.’’
Some of the most closely watched Senate races pitted centrist Democrats against conservative Republicans who ardently embraced Trump. Contests in Missouri, North Dakota, Indiana, West Virginia, and Tennessee fell into this category.
Even before Tuesday’s vote, Senate Republicans were poised for a more pro-Trump roster next year. Senators Jeff Flake, Republican of Arizona, and Bob Corker, Republican of Tennessee, who have frequently voiced concerns about Trump’s tone and his governing philosophy, are retiring. John McCain, a vocal Trump critic, died in August.
Democrats tried to defeat candidates who marched in lockstep with Trump by running on preserving health-care protections and other so-called kitchen table issues. In key races, they fell short.
In North Dakota, Cramer’s defeat of Senator Heidi Heitkamp means that one of the chamber’s few moderate Democrats will be replaced by a close ally of Trump. Trump personally recruited Cramer to run. On major issues, Cramer endorsed Trump’s positions.
In Indiana, Braun ran in Trump’s mold, as an outsider eager to shake up Washington. He defeated a pair of House members in the Republican primary before beating centrist Democratic Senator Joe Donnelly on Tuesday.
Two states over in Missouri, Republican state Attorney General Josh Hawley ousted Senator Claire McCaskill, a Democrat, in a race with similar dynamics. Hawley, like Cramer, championed Trump’s views on trade, even as he faced criticism that farmers in his state would suffer under the president’s tariffs.
One wild card next year is Mitt Romney. The former Republican presidential nominee won the seat of retiring GOP Senator Orrin Hatch. Romney has criticized Trump, including in a speech opposing his candidacy in 2016. But lately, he has been less openly hostile to the president.
Senate Democrats were defending 26 of the 35 seats on the ballot, including 10 in states Trump won. They were hoping to offset their losses with some gains.
They looked to pick up a pair of seats in the Sun Belt, with Representative Jacky Rosen, Democrat of Nevada, trying to unseat Senator Dean Heller, Republican of Nevada, a onetime Trump critic who warmed up to the president during the campaign.
In Arizona, Democratic leaders were hopeful that Representative Kyrsten Sinema, a former Green Party activist who ran as moderate Democrat, would win Flake’s seat. Her opponent was Representative Martha McSally, a onetime Trump critic who dialed down her hostility in the campaign.
Florida, another state with a diverse population, was the site of the expensive and pivotal showdown between Senator Bill Nelson, a Democrat, and Governor Rick Scott, a Republican. Scott, unlike most other top Senate candidates, distanced himself from the president in the campaign. The race was tight late Tuesday.
Many Democratic Senate contenders railed against Trump’s tariffs during the campaign. In Tennessee, former governor Phil Bredesen, who lost to Blackburn, cast the tariffs as harmful to the state’s automobile, farming and whiskey industries.
Senator Joe Manchin, a Democrat, held onto his seat in West Virginia. Manchin was the only Democrat to vote for Supreme Court Justice Brett Kavanaugh. He has touted his cooperation with the president and Republicans are expected to court his support in future votes.
Democrats were hopeful Jon Tester, Democrat of Montana, would keep his seat, despite Trump holding a rally in his state in the final stage of the campaign.
Senator Ted Cruz, Republican of Texas,, who clashed sharply with Trump in the 2016 primary, lined up squarely behind the president en route to his defeat of Representative Beto O’Rourke, a Democrat, who achieved rock star status on the left.