The conservative political action committee Club for Growth has said it will back Mr. Mooney in the primary. Joe Kildea, a spokesman for the group, said its political arm had raised about $14 million and would spend “whatever it takes.” That could bloody Mr. Justice, but money alone may not be enough for Mr. Mooney, who trails the governor among West Virginia Republican voters, 58 percent to 26 percent.
“We beat big-government, establishment RINOs all the time,” said David McIntosh, the president of Club for Growth, referring to the conservative slur “Republicans in name only.”
It is also unclear whether Mr. Trump will seek to get involved in the primary, set for May 14. In 2022, he endorsed Mr. Mooney in a House Republican primary against Representative David B. McKinley, and Mr. Mooney won easily. This time around, Mr. Trump is extremely unhappy with Club for Growth, which has funded an advertising campaign in Iowa imploring Republicans to back a different presidential candidate. Then again, he also likes to counter Senator Mitch McConnell of Kentucky, the minority leader, who backs Mr. Justice.
Mr. Manchin’s allies claim that none of that is weighing particularly heavily on the senator these days.
“I know it’s shocking in D.C., but Joe Manchin isn’t focused on partisan politics this year,” said Jonathan Kott, his former senior adviser in the Senate. “He will sit down with his family at the end of the year and figure out how he can best serve the people of West Virginia and the country.”