Sen. John McCain John Sidney McCainBiden's six best bets in 2016 Trump states Replacing Justice Ginsburg could depend on Arizona's next senator The Hill's Morning Report - Sponsored by Facebook - Washington on edge amid SCOTUS vacancy MORE (R-Ariz.) will return to the Senate on Tuesday after being diagnosed with brain cancer, giving the GOP push to repeal and replace ObamaCare a boost of momentum.

“Senator McCain looks forward to returning to the United States Senate tomorrow to continue working on important legislation, including health care reform, the National Defense Authorization Act, and new sanctions on Russia, Iran and North Korea," McCain's office said on Monday evening.

McCain was absent last week after having surgery to remove a blood clot from above his left eye, which then revealed his cancer.

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Look forward to returning to Senate tomorrow to continue work on health care reform, defense bill & #RussiaSanctions https://t.co/VQBtovnwF1 — John McCain (@SenJohnMcCain) July 25, 2017

If McCain hadn't returned, McConnell could only afford to lose one GOP senator on the initial hurdle. With McCain back, he can afford to lose two GOP senators and still let Vice President Pence break a tie.

McCain's office didn't immediately respond to a request for comment on how he would vote on the initial procedural motion. But McCain called late last week for his conference to go back to the drawing board and send a healthcare bill through "regular order." "The Congress must now return to regular order , hold hearings, receive input from members of both parties, and heed the recommendations of our nation's governors so that we can produce a bill that finally provides Americans with access to quality and affordable health care," he said in a statement last week.

McConnell sparked speculation Monday evening that McCain would be returning soon when he teed up the National Defense Authorization Act (NDAA), an annual bill McCain crafts as chairman of the Senate Armed Services Committee.

Leadership had indicated that they wanted to wait until McCain returned to the Senate to try to move the NDAA.