Texas Attorney General Ken Paxton enters the May 26 Republican primary runoff against Sen. John Cornyn (R-TX) with a fundraising gap that could prove fatal to his campaign.

And unusually for a race of this size, Paxton allies are pointing the finger at a single donor: Leonard Leo, the conservative powerbroker sitting atop a reported $1 billion-plus war chest, large portions of which he had previously deployed to make Paxton the GOP political force he is today, but which are now parked safely on the sidelines as Paxton faces the toughest fight of his political life.