Americans for Prosperity, a fundraising organization established by powerful conservatives Charles and David Koch, is not endorsing former President Donald Trump in the 2024 Republican primary, the organization implied in a memo Sunday.

“The best thing for the country would be to have a president in 2025 who represents a new chapter,” a letter from the organization’s CEO, Emily Seidel, said. But the memo didn’t mention Trump by name, leaving open the possibility of an endorsement further down the road.

The move could mark trouble for Trump, if it leads the AFP’s base of wealthy conservative donors away from his campaign. He is the only candidate from a major party to announce a 2024 run so far, though a cast of potential Republican challengers have publicly teased potential campaigns.