The donor network created by the billionaire industrialist brothers Charles G. and David H. Koch is preparing to get involved in the presidential primaries in 2024, with the aim of turning “the page on the past” in a thinly veiled rebuke of former President Donald J. Trump, according to an internal memo.

The network, comprising an array of political and advocacy groups that have been backed by hundreds of ultrawealthy conservatives, has been among the most influential forces in American politics over the past 15 years, spending nearly $500 million supporting Republican candidates and conservative policies in the 2020 election cycle alone. But it has never before supported candidates in presidential primaries.

The potential move against Mr. Trump could motivate donors to line up behind another prospective candidate. Thus far, only the former president has entered the race.

The memo went out to the affiliated activists and donors after a weekend conference in Palm Springs, Calif., where the network’s leaders laid out their goals for the next presidential election cycle. At various sessions, they made clear they planned to get involved in primaries for various offices, and early.

“The Republican Party is nominating bad candidates who are advocating for things that go against core American principles,” the memo declares. “And the American people are rejecting them.” It asserts that Democrats are responding with “policies that also go against our core American principles.”

The memo’s author is Emily Seidel, chief executive of the lead nonprofit group in the network, Americans for Prosperity, and an adviser to an affiliated super PAC. But the principles sketched out in the memo are expected to apply to some other groups in the network, which is now known as Stand Together.

Americans for Prosperity’s super PAC spent nearly $80 million during the 2022 midterm elections, but that is likely just a fraction of the network’s overall spending, much of which was undertaken by nonprofit groups that will not be required to reveal their finances until this fall.

One of the lessons learned from primary campaigns in the 2022 midterm election cycle, the memo says, in boldface, “is that the loudest voice in each political party sets the tone for the entire election. In a presidential year, that’s the presidential candidate.”

It continues, “And to write a new chapter for our country, we need to turn the page on the past. So the best thing for the country would be to have a president in 2025 who represents a new chapter. The American people have shown that they’re ready to move on, and so A.F.P. will help them do that.”

Though the memo did not mention Mr. Trump’s name, leaving open the possibility that the network could fall in behind him if he won the Republican nomination, its references to a “new chapter” and leaving the past behind were unmistakable.

Mr. Trump’s early entry into the race, in November, has largely frozen the field. The only other candidate expected to get into the race soon is Nikki Haley, the former governor of South Carolina, whose allies, despite her work as the U.N. ambassador under Mr. Trump, have cast her as a change from the past.

Mr. Trump’s early campaign has not shown the financial dominance he did as a nominee, and a number of major donors have made clear they are not inclined to support him over other candidates. The Club for Growth, the anti-tax group that was once aligned with Mr. Trump, has split with him and is said to be interested in opposing his candidacy.

It remains to be seen how successful the Koch group will be marshaling resources behind a single candidate, or if Charles Koch will donate significantly himself. But at minimum, the development is the latest indication that traditional aspects of the Republican ecosystem are less fearful of Mr. Trump than they had been.

The Koch network publicly opposed some of Mr. Trump’s policies, including tariffs he imposed as president, though it worked with his administration on an overhaul of the criminal justice system that slashed some sentences.

If the network were to unite behind an alternative to Mr. Trump, it could give that candidate a tremendous boost, given the resources at its disposal, which at times have rivaled — and even surpassed — those of the Republican National Committee.

It would also be a stark departure for the Koch network, which was begun by the Koch brothers during former President George W. Bush’s administration as an effort to reorient the Republican Party and American politics around their libertarian-infused conservatism.

A number of the party’s most prolific donors have remained on the sidelines, with a Republican primary field that has yet to take shape.

The network has had ties to former Vice President Mike Pence, who is taking steps that could lead to a presidential campaign. And some major donors have expressed interest in Gov. Ron DeSantis of Florida, who is also weighing a potential campaign. But if Mr. DeSantis enters the race, he is likely months away from doing so, according to people familiar with his thinking.

A number of big donors who backed Mr. Trump in 2016 and 2020 have yet to say they will do so again. Other groups of donors, such as those belonging to the hedge fund billionaire Paul Singer’s American Opportunity Alliance, which overlaps with the Koch network, are also largely on the sidelines so far.

It may be easier for the Koch network to decide to oppose Mr. Trump than to agree on an alternative.

In past election cycles, the ideological diversity of the network’s donors, as well as the Kochs’ commitment to their own ideology, have been impediments to uniting behind a single presidential candidate.

While Charles Koch is the most prominent figure in the network — his brother David began stepping back from it before his death in 2019 — it draws its influence partly from its ability to pool resources from an array of major donors who represent sometimes divergent wings of the Republican Party, including noninterventionists, foreign policy hawks and religious conservatives.

Perhaps the closest the network came to wading into a Republican presidential nominating contest was in 2016, when it was pressured by some donors and operatives to back an opponent of Mr. Trump, who was seen as anathema to the Kochs’ limited government, free-trade instincts.

But the network wavered. And one of its top operatives, Marc Short, decamped for the presidential campaign of Senator Marco Rubio of Florida, who was viewed by many Koch-aligned donors as having the best chance to defeat Mr. Trump, but whose hawkish instincts ran afoul of the Kochs.

The network remained largely on the sidelines of the 2016 presidential race after Mr. Trump won the Republican nomination: Charles Koch at one point compared having to decide whether to support Mr. Trump or Hillary Clinton, the Democratic nominee, to being asked to choose between cancer or a heart attack.

It continued to sit out presidential politics in 2020, when Mr. Koch expressed regret over the network’s financial backing of Republicans and proclaimed that it had “abandoned partisanship” in favor of bipartisan efforts like overhauling the criminal justice system.

While the network has cast itself as motivated by issues, not partisanship, and has expressed willingness to support Democrats who align with it on some policies, its federal election spending has almost exclusively gone toward Republicans.

Ms. Seidel wrote in the memo that “it looks like the Democrats have already chosen their path for the presidential — so there’s no opportunity to have a positive impact there.” Americans for Prosperity’s super PAC, she added, “is prepared to support a candidate in the Republican presidential primary who can lead our country forward, and who can win.”

Ms. Seidel also rejected the idea that the network had retreated from politics, noting in the memo that Americans for Prosperity engaged in more primary elections last year — about 200 at the state and federal level — than ever before, and that the candidates it supported won in more than 80 percent of those races.