Trump Strengthens Grip on Capitol Hill as He Presses Toward Nomination

For months, Senate Republicans have been working with Democrats on a deal they have described as a once-in-a-generation opportunity for a conservative border security bill, and for weeks, they have hinted that they are tantalizingly close to an agreement.

Their timing could not be worse.

As former President Donald J. Trump moves closer to becoming his party’s presidential nominee and Republican lawmakers consolidate behind him, he is wielding a heavier hand than any time since leaving office over his party’s agenda in Congress. His vocal opposition to the emerging border compromise has all but killed the measure’s chances in a divided Congress as he puts his own hard-line immigration policies once again at the center of his presidential campaign.

His shadow has always loomed large over the Republican-controlled House, which has opened congressional investigations to defend him, launched an impeachment inquiry into his chief rival and approved legislation to reinstate the hard-line immigration policies he imposed. But as Mr. Trump barrels toward the party’s 2024 nomination, his influence on the legislative agenda on Capitol Hill is expanding.

His “America First” approach to foreign policy already helped to sap G.O.P. support for sending aid to Ukraine for its war against Russian aggression, placing the fate of that money in doubt. That led Republicans to demand a border crackdown in exchange for any further funding for Kyiv, a compromise that Mr. Trump has now repudiated. He frequently consults with the inexperienced Speaker Mike Johnson, weighing in on policy and politics. And his uncompromising approach has emboldened copycat politicians in Congress, like Representatives Marjorie Taylor Greene of Georgia and Matt Gaetz of