Sen. Rand PaulRandal (Rand) Howard PaulTim Scott sparks buzz in crowded field of White House hopefuls Sherrod Brown calls Rand Paul 'kind of a lunatic' for not wearing mask Overnight Health Care: WHO-backed Covax gets a boost from Moderna MORE (R-Ky.) said early Tuesday that the GOP presidential primary’s rules favor the Republican establishment.

“I hear someone’s been saying that they’re rigged,” he said on MSNBC, referencing GOP presidential front-runner Donald TrumpDonald TrumpSanders: Reinstating SALT deduction 'sends a terrible, terrible message' GOP braces for wild week with momentous vote One quick asylum fix: How Garland can help domestic violence survivors MORE.

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“They’re not rigged – they’re biased,” Paul added. "Rigged would mean that they’re illegal or shady. It’s done somewhat in favor of the establishment.”

Trump on late Monday attacked the GOP’s primary rules, arguing that they are “rigged, disgusting [and] dirty.”

The businessman is unhappy with his party’s nominating requirements, which have let Ted CruzRafael (Ted) Edward CruzCheney drama exposes GOP's Trump rifts Pollster Frank Luntz: 'I would bet on' Trump being 2024 GOP nominee Tim Scott sparks buzz in crowded field of White House hopefuls MORE remain competitive despite trailing in delegates and voter support.

Paul on Tuesday said that establishment Republicans are always concerned with preserving their political power.

“We don’t always know who the establishment is, [but] there’s always people trying to change the rules to their advantage,” said Paul, who suspended his own White House run last February.

Paul also said that Trump and Cruz must watch for significant changes in the Republican National Convention’s rules next July.

“Both Cruz and Trump have a great deal of incentive to not let anyone else have any of their votes,” he said.

“My understanding of the rules is that if they follow the precedent of 2012, Rubio and Kasich’s votes aren’t counted,” Paul added, referencing Sen. Marco RubioMarco Antonio RubioDemocrats cool on Crist's latest bid for Florida governor Tim Scott sparks buzz in crowded field of White House hopefuls The unflappable Liz Cheney: Why Trump Republicans have struggled to crush her  MORE (R-Fla.) and Gov. John Kasich (R-Ohio).

Rubio suspended his presidential campaign last month, while Kasich remains in the race for the Republican presidential nomination.

Trump leads Cruz by roughly 7 points nationwide, according to the latest RealClearPolitics average of polls. He also has 743 delegates to Cruz’s 545.