Sen. Rand PaulRandal (Rand) Howard PaulRon Paul hospitalized in Texas The Hill's Morning Report - Sponsored by Facebook - Trump previews SCOTUS nominee as 'totally brilliant' Rand Paul says he can't judge 'guilt or innocence' in Breonna Taylor case 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 John TrumpCensus Bureau intends to wrap up count on Oct. 5 despite judge's order Top House Republican calls for probe of source of NYT Trump tax documents New Yorkers report receiving ballots with wrong name, voter addresses 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 CruzSupreme Court fight should drive Democrats and help Biden Fears grow of chaotic election Senate GOP set to vote on Trump's Supreme Court pick before election 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 RubioGOP online donor platform offering supporters 'Notorious A.C.B.' shirts Sunday shows preview: Lawmakers prepare for SCOTUS confirmation hearings before election GOP lawmakers distance themselves from Trump comments on transfer of power 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.