Sen. Rand PaulRandal (Rand) Howard PaulGraham promises ObamaCare repeal if Trump, Republicans win in 2020 Conservatives buck Trump over worries of 'socialist' drug pricing Rand Paul to 'limit' August activities due to health 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 TrumpSarah Huckabee Sanders becomes Fox News contributor The US-Iranian scuffle over a ship is a sideshow to events in the Gulf South Korea: US, North Korea to resume nuclear talks 'soon' 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 CruzGOP strategist predicts Biden will win nomination, cites fundraising strength 3 real problems Republicans need to address to win in 2020 The Hill's Morning Report - Trump on defense over economic jitters 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 group calls on Republican senators to stand up to McConnell on election security in new ads What the gun safety debate says about Washington Trump moves forward with F-16 sale to Taiwan opposed by China 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.