Sen. John McCain, R-Ariz., is set to miss the key vote on the Republican-backed tax bill as he travels back to Arizona to continue recovering from side effects brought on by his chemotherapy treatment.

McCain left for Arizona on Sunday from Maryland, where he had been hospitalized.

CBS News reported McCain will remain in Arizona through the holidays, meaning he will miss any votes planned in the coming days.

That will complicate President Trump and the GOP's plans to pass the tax bill, which is already barely supported by enough Republicans, ahead of the holiday recess. The GOP can afford just two defections while Sen. Luther Strange, R-Ala., remains in office. Strange is set to be replaced by Senator-elect Doug Jones, a Democrat, once the election results in Alabama are certified, further shrinking the Republican majority.

It's widely believed the Republicans will have enough votes to pass the bill.

McCain was diagnosed earlier this year with brain cancer.