The political network founded by the billionaire industrialist brothers Charles and David Koch has endorsed Nikki Haley in the Republican presidential nominating contest, giving her organizational muscle and financial heft as she battles Gov. Ron DeSantis of Florida to be the top rival to former President Donald J. Trump.

The group announced its plans in a memo on Tuesday.

The commitment by the network, Americans for Prosperity Action, bolsters Ms. Haley as the campaign enters the final seven weeks before the Iowa caucuses.

Since the first Republican primary debate, Ms. Haley has steadily climbed in polls, even as Mr. DeSantis has slipped.

Mr. Trump remains the dominant front-runner in the race.

“In sharp contrast to recent elections that were dominated by the negative baggage of Donald Trump and in which good candidates lost races that should have been won, Nikki Haley, at the top of the ticket, would boost candidates up and down the ballot,” reads the memo from Emily Seidel, a senior adviser to Americans for Prosperity Action, who adds that Ms. Haley would win “the key independent and moderate voters that Trump has no chance to win.”

The memo goes on to say that the country “is being ripped apart by extremes on both sides,” adding: “The moment we face requires a tested leader with the governing judgment and policy experience to pull our nation back from the brink. Nikki Haley is that leader.”.