In a sign of a worsening climate, Democratic officials shifted money to incumbents in once-safe districts around Las Vegas and Santa Barbara, Calif. And over the weekend, they put more money toward television ads in districts held by Democrats in Iowa and Minnesota, including that of longtime Representative Collin C. Peterson of Minnesota. Though there are fewer competitive House seats than in past elections because of gerrymandering, party strategists were still airing ads in 40 districts.

“It’s a grim environment,” said Representative Steve Israel of New York, the chairman of the Democratic Congressional Campaign Committee. Mr. Israel was spending the weekend pleading with his caucus to contribute to imperiled colleagues to minimize losses. Trying to soften the blow, he noted that losses were expected: The party in control of the White House has lost an average of 29 seats in midterm elections in the last century…

Senate Republicans are confident. A senior party official called Senator Mitch McConnell of Kentucky, the minority leader, on Saturday at his Louisville home and, after running through voting projections, told Mr. McConnell that he would be the next majority leader. Mr. McConnell’s initial reaction was only a long pause.