Sen. Rand PaulRandal (Rand) Howard PaulFox News legal analyst says quid pro quo is 'clearly impeachable': Trump requested 'criminal' act Federal court rules baseless searches of travelers' devices unconstitutional Sunday shows — New impeachment phase dominates 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 TrumpTrump faces high stakes in meeting with Erdoğan amid impeachment drama Democrats worry they don't have right candidate to beat Trump Trump threatening to fire Mulvaney: report 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 CruzTrump circuit court nominee in jeopardy amid GOP opposition Trump has officially appointed one in four circuit court judges On The Money: Retirement savings bill blocked in Senate after fight over amendments | Stopgap bill may set up December spending fight | Hardwood industry pleads for relief from Trump trade war 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 senators plan to tune out impeachment week Republicans warn election results are 'wake-up call' for Trump Paul's demand to out whistleblower rankles GOP colleagues 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.