WASHINGTON — Senate Republicans will face a final pre-election test Thursday over President Donald Trump’s war in Iran, as rising fuel prices increase pressure on lawmakers in competitive races. Democrats are expected to bring a nonbinding war powers resolution to the floor before Congress leaves Washington until after the midterm elections. At least four Republicans — Susan Collins of Maine, Lisa Murkowski of Alaska, Rand Paul of Kentucky and Thom Tillis of North Carolina — are expected to support it. With Sen. John Fetterman, D-Pa., expected to oppose the measure, Democrats need one additional Republican vote for passage if all senators attend. The resolution would not require Trump’s signature, but a successful vote would represent a public rebuke of his military policy and put Republican senators on record about the nearly eight-month conflict. Trump has previously expressed anger over Republican defections on similar measures. Sen. Bill Cassidy, R-La., who is retiring, said Wednesday that he had not decided how he would vote. Cassidy said he had spoken with administration officials but declined to characterize his position as either yes or no. Senate Majority Leader John Thune, R-S.D., said Republican leaders were monitoring the vote and hoped the caucus would remain united. The prospect of defections underscores the political strain facing Republicans who are trying to distance themselves from the war’s economic consequences without directly breaking with Trump. Several Republican candidates and lawmakers have called for the conflict to end as fuel prices rise. Sen. Jon Husted, R-Ohio, said this week that the war should conclude quickly so gas prices can fall, but he is not expected to support the resolution. Husted is running in a competitive race against former Democratic Sen. Sherrod Brown. Sen. Dan Sullivan, R-Alaska, has proposed temporarily banning diesel imports for the duration of the conflict, a measure some Republicans say could reduce costs. His office did not say how he would vote on the resolution. Sen. John Curtis, R-Utah, is also expected to oppose it, with an aide citing concerns that an abrupt end to the war could create national-security risks. Thune acknowledged that candidates in difficult races may need to craft messages tailored to their states. He said the immediate economic concern was voter frustration over high gas prices and called on the administration to reopen shipping lanes and improve global energy supplies. The political concern extends beyond the Senate. Former Rep. Mike Rogers, who is seeking a Michigan Senate seat, Rep. Ashley Hinson, who is running in Iowa, and Rep. John James, a Republican candidate for Michigan governor, have called for the war to end. Iowa Reps. Mariannette Miller-Meeks and Zach Nunn recently voted for a House resolution seeking to end the conflict. Sen. Joni Ernst, R-Iowa, said lawmakers need a clear administration plan for ending the war and acknowledged that the conflict is affecting people’s daily lives. She nevertheless said she would probably continue opposing war powers resolutions. Ernst and other Senate Armed Services Committee members received a classified briefing Wednesday from Adm. Brad Cooper, the head of U.S. Central Command. Senators said the briefing covered military readiness and ammunition supplies but did not provide a firm timeline for ending the conflict. Sen. Tommy Tuberville, R-Ala., said officials offered no concrete answer on when the war would conclude. The lack of an end strategy has frustrated some Republicans who support the administration’s policy, particularly after Trump’s earlier predictions that the fighting would last only a few weeks. The vote is therefore about more than congressional procedure. It will test whether Republicans are willing to challenge the president as voters confront the costs of a prolonged war — and whether concerns about fuel prices are strong enough to overcome pressure to keep the party aligned before the midterms.