The political environment has worsened for Republicans as they try to defend control of Congress, though the party has a big cash advantage over Democrats. Republicans are putting up a costly defense of states and districts that President Trump won easily in 2024. In Georgia, Republican strategists are privately discussing whether the Senate race has drifted beyond the party’s reach.

In Kansas, Vice President JD Vance campaigned for a Senate Republican, even though a Democrat there has not been elected to the chamber since 1932. In Nebraska, a new Republican super PAC just sprang up to spend to defend a billionaire incumbent. Across the country, President Trump’s political operation is investing in once-bright-red races, including several in Texas that his party claimed to have safely gerrymandered only a year ago.

Less than seven weeks before the midterms, the battlefield now extends deep into states and districts Mr. Trump carried three times, often by double digits. Senator Chuck Schumer said Democrats feel confident but cautioned the map is not easy. Mr. Trump’s diminished standing and voter anger about high prices from tariffs and the war with Iran are causing serious problems. The Federal Reserve raised interest rates, increasing borrowing costs.

Speaker Mike Johnson acknowledged high gas and diesel prices tied to the Strait of Hormuz. A New York Times and Siena University poll shows Democrats with a nearly nine-point advantage on the congressional ballot, similar to 2018. Representative Hakeem Jeffries said Republicans are panicking and on the brink of losing the House, with the Senate not far behind.

Republicans have a big cash advantage, using it for attack ads from South Florida to Alaska. Republican super PACs, led by Mr. Trump’s network, have booked over $140 million in advertising since Labor Day. Representative Richard Hudson said voters weren’t paying attention until after Labor Day, and now they’re turning everything on.

The first big state that could fall off the map for Republicans is Georgia, where Senator Jon Ossoff holds the Democrats’ most endangered seat.