Forty days before the midterm elections, a growing number of Republican candidates are openly seeking to distance themselves from President Trump, breaking with a leader who has long held an iron grip on his party.

On Monday, Republican Senate candidates in Michigan and Iowa called on the president to end the war in Iran to reverse escalating gas prices. By Tuesday, G.O.P. candidates for governor in Wisconsin and Michigan, along with an embattled Republican senator in Ohio, followed. "The war with Iran needs to end — and end quickly," said former Representative Mike Rogers, the Republican Senate nominee in Michigan.

On Capitol Hill, three Republican senators called for an investigation into the president's son over his lavish wedding after-party paid for by a Russian businessman with ties to President Vladimir V. Putin. In Florida, Representative Byron Donalds, the Republican nominee for governor, overhauled his website to make Mr. Trump's endorsement less prominent.

Mr. Trump's approval rating is languishing near record lows, with his economic approval hitting 27 percent in a CNN poll. Marc Short, who served as White House legislative affairs director in Mr. Trump's first term, said the distancing is more pronounced than in 2018 and "does feel somewhat like desperation." White House spokesman Davis Ingle disputed any distance, calling Mr. Trump "the unequivocal leader" of the Republican Party.