On Election Day in 2016, the Republican Party was divided against itself, split over its nominee for president, Donald J. Trump.

In Ohio, a crucial battleground, the state party chairman had repeatedly chided Mr. Trump in public, amplifying the concerns of Gov. John Kasich, a Republican dissenter. In New Hampshire, the party chairman harbored deep, if largely private, misgivings about her party’s nominee. The Republican Party of Florida was listing, hobbled by local feuds and a rift between donors loyal to Senator Marco Rubio and former Gov. Jeb Bush and those backing the man who humiliated both in the primaries.

Those power struggles have now been resolved in a one-sided fashion. In every state important to the 2020 race, Mr. Trump and his lieutenants are in firm control of the Republican electoral machinery, and they are taking steps to extend and tighten their grip.

It is, in every institutional sense, Mr. Trump’s party.

As Mr. Trump has prepared to embark on a difficult fight for re-election, a small but ferocious operation within his campaign has helped install loyal allies atop the most significant state parties and urged them to speak up loudly to discourage conservative criticism of Mr. Trump. The campaign has dispatched aides to state party conclaves, Republican executive committee meetings and fund-raising dinners, all with the aim of ensuring the delegates at next year’s convention in Charlotte, N.C., are utterly committed to Mr. Trump.