Former CBS News anchor Dan Rather is predicting that some Republicans could defect from President Trump if his poll numbers slip below 30 percent.

"They're afraid that he may have indeed committed some impeachable offense, and also they're hearing from home that a lot of their constituents have increasing concerns about the Trump presidency," Rather told CNN's Don Lemon.

"As long as he's able to hold that 35, 38 poll rating – you may not see that, but I repeat for emphasis, once it gets down below 30 percent, you'll see some Republicans going the other way," said the longtime host.

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Despite being saddled with a steady stream of controversies and consistently low approval ratings in his first months in office, Trump has largely maintained the backing of GOP lawmakers.

Trump's approval rating currently sits at 39 percent, according to a Real Clear Politics average of presidential job approval ratings. Among Republicans, his approval rating is much higher.

The president has faced mounting controversies, particularly related to the ongoing law enforcement investigation into Russian election meddling and possible collusion between his election campaign and Russia. Trump has repeatedly called the probe a "witch hunt" and has denied any wrongdoing.

The latest controversy came on Thursday, when fired FBI Director James Comey told lawmakers during a congressional hearing that Trump had once asked him in private conversation for a pledge of loyalty and then to drop the bureau's investigation of former national security adviser Michael Flynn.

Republican lawmakers, including House Speaker Paul Ryan Paul Davis RyanKenosha will be a good bellwether in 2020 At indoor rally, Pence says election runs through Wisconsin Juan Williams: Breaking down the debates MORE (R-Wis.), acknowledged that the president's requests may have been inappropriate, but defended his actions as rookie mistakes – the result of Trump's lack of government experience.

But some of Trump's highest-profile policies have spurred backlash, as well. His decision last week to withdraw the U.S. from the Paris climate accord, for example, sparked nationwide protests and prompted vows by numerous business leaders, governors and mayors to uphold the agreement in spite of Trump's announcement.

A Washington Post-ABC News poll conducted in the wake of Trump's decision found that nearly six in 10 Americans oppose withdrawing from the climate deal.