Donald J. Trump’s dominance in the Republican primary is upending the campaign for control of Congress, as Republican lawmakers seek to distance themselves from him while Democrats seize on the chance to run against a candidate who has offended huge sections of the American electorate. Nominating Mr. Trump could create a political battlefield of extraordinary breadth and volatility. Polling shows that he would enter the general election trailing badly against Hillary Clinton, and he has become deeply unpopular outside of his white, heavily male political base. While Mr. Trump would most likely draw throngs of white, working-class voters in Democratic-leaning states like Michigan and Ohio, he would also drive away women, nonwhites and voters with college degrees in conservative-leaning states like Georgia and North Carolina. Both parties are now racing to gauge the impact further down the ballot of a candidacy that could shatter traditional lines of combat in national politics. Former Senator Norm Coleman of Minnesota, an influential Republican strategist and fund-raiser, said Mr. Trump’s nomination could imperil even the party’s seemingly iron grip on the House. Mr. Coleman said major donors were increasingly focused on building a “firewall” around Congress, because they believe Democrats would easily defeat Mr. Trump and keep control of the White House. “Everything is in play: the presidency, the Supreme Court, the Senate and potentially the House,” he said. Mr. Coleman said Republicans would have to decide on a case-by-case basis how to handle Mr. Trump in their races. “If it were me and I were running, and Trump were going to be at the top of the ticket, I would disavow him,” he said. Republicans, who hold the Senate 54 to 46 and maintain control of the House by 30 seats, believe it would be essential for candidates running in diverse or comparatively affluent areas to break with Mr. Trump on matters of policy, and perhaps to denounce his nomination in blunt terms. With control of the Senate resting in large part on Democratic-leaning states like Pennsylvania and Wisconsin, Republicans are preparing to run aggressively localized campaigns aimed at persuading voters to split their ballot for a Republican senator even if they support a Democrat for president. Some party leaders remain hopeful that they can block Mr. Trump by denying him a majority of the delegates to the July convention and coalescing support around another candidate. But the National Republican Senatorial Committee has already conducted polling to test the message that Republicans must control the Senate as a check against a President Hillary Clinton, and that Democrats must not be allowed to fully control the appointment and confirmation of Supreme Court judges, according to two people briefed on the research, who spoke on the condition of anonymity because it was intended to be confidential. Democrats see Mr. Trump as increasing their chances, especially in diverse and fast-growing states like Arizona and Virginia, where the party often struggles to turn out Hispanic voters who can help its candidates. And the Democratic Congressional Campaign Committee is mounting a late push to stretch the political map by recruiting candidates in as many as 10 conservative-leaning House districts, in states like Florida and Kansas, where analysts believe Mr. Trump will harm Republicans. The Democratic committee, eager to cut into the Republicans’ majority, has begun a large data project to model both support for and opposition to Mr. Trump. Meredith Kelly, a spokeswoman for the committee, confirmed that its data team was studying which of Mr. Trump’s ideas and comments would be most offensive to key voting blocs, and how best to project those themes in congressional races. Gov. Dannel P. Malloy of Connecticut, chairman of the Democratic Governors’ Association, said Republicans had a no-win situation on their hands: They could either run from Mr. Trump and risk depressing Republican turnout, or embrace him and have to defend “views that are abhorrent” to many people. “Quite frankly, we’re going to hold people accountable: Are you with Trump and his policies, or are you against him?” Mr. Malloy said.

• published: 29 Mar 2016
• views: 6