Donald Trump fears he may lose in November because of the "rigged" political system he's been railing against for months.

"I'm afraid the election is going to be rigged, I have to be honest," Trump told supporters during a mid-afternoon rally in Columbus, Ohio.

Trump has blasted political leaders for creating what he claims is a corrupt and "crooked" system under which career politicians have manipulated certain rules and deliberately lied to voters in order to remain in power.

At one point during the primary, the Republican presidential nominee threatened to sue the Louisiana GOP over its "unfair" delegate allocation rules. Trump also accused Democrats of rigging their own nominating contest to deny Vermont Sen. Bernie Sanders a legitimate chance at beating Hillary Clinton.

Monday was the first time, however, that Trump has claimed the general election might be rigged in favor of his Democratic opponent. The suggestion came minutes before a new national CNN/ORC survey showed him trailing Clinton 45 to 37 percent.

Trump will hold his second rally of the day in Mechanicsburg, Pa., at 7 p.m. ET.