President Trump is harnessing the Republican Party’s all-encompassing deference to him to exert even greater control over the G.O.P. big-money world, which had long been one of the party’s final remaining redoubts of Trump skepticism.

For years, the super PACs allied with House and Senate Republicans have been some of the most powerful and independent fiefs in American politics, raising and spending hundreds of millions of dollars in each election.

But even though Mr. Trump is in his second term and cannot run again, he is quickly bringing them inside his sphere of influence — a sign that his dominance over the party could endure well into the future.

Both super PACs, the Congressional Leadership Fund and the Senate Leadership Fund, have new leaders this year, and they are working closer than ever with the White House, overhauling their boards of directors and installing veteran Trump strategists in senior positions.

At the same time, Mr. Trump’s super PAC, MAGA Inc., and its allied nonprofit group have already amassed roughly $400 million since the 2024 election, according to two people briefed on the fund-raising who insisted on anonymity to discuss the organization’s finances. That sum is without precedent so early in an election cycle, especially for a termed-out president. The Trump super PAC is expected to play a major role in the midterm elections, scrambling the usual flow of cash and encroaching on the traditional dominion of the congressional super PACs.

The changes — both in personnel and financial firepower — amount to a fundamental reordering of Republican finance, and an extraordinary expansion of Mr. Trump’s already overwhelming sway. Interviews with senior Republicans allied with leaders on Capitol Hill reveal private fears about a power imbalance if the G.O.P.’s top super PACs are weakened and overly submissive to Mr. Trump.