U.S. Senator Thad Cochran will not return to Washington Monday, setting off alarms about the senator’s future in both Washington and Jackson.

Cochran, who has been at his Oxford home since September after undergoing a urological medical procedure, said two weeks ago and again on Friday that the senator would return to Washington on Monday.

But the 79-year-old senator was still too ill to return today.

“Mrs. Cochran informed me late Saturday night that Sen. Cochran has developed another urinary tract infection,” said Brad White, Cochran’s chief of staff. “After a day of monitoring his condition, and on the advice of his physicians and other health care professionals, Sen. Cochran has postponed his return to Washington.

“The senator has expressed his intention to return to the Senate when his health permits, and to fulfill his commitment and duties to the people of his state.”

As chairman of Senate Appropriations committee, Cochran plays a key role in finalizing the federal government’s budget. This year’s deadline to finish the budget before a government shutdown is mid-December.

The Senate reconvenes today after a recess, and Cochran had been scheduled on Thursday to lead an Appropriations committee meeting, in which committee members will continue marking up next year’s budget.

Cochran’s vote on the Senate floor also is important as Senate Majority Leader Mitch McConnell, R-Ky., continues to push for tax and budget cuts. Three absent or no Republican votes could stall or kill legislation.

Cochran’s health has been the subject of speculation several times since his 2014 election. In September, President Donald Trump tweeted that Cochran was in the hospital when Republicans were trying to repeal the Affordable Care Act. Cochran took to Twitter himself to dispute the claim, saying he was home in Oxford recovering from the urinary infection.

Adding to Republicans’ concern over Cochran’s status, the establishment wing of the party already faces stiff challenges from more conservative Republicans in the 2018 midterm elections. In that race, Sen. Roger Wicker, Mississippi’s junior senator, has been named as a target in 2018. Sen. Bob Corker, R-Tenn., already has announced his retirement.

Another unexpected vacancy — in deep red Mississippi, nonetheless — could be a headache for an already reeling Republican leadership. All eyes will turn to the governor’s mansion.

If Cochran’s seat becomes vacant before Nov. 6, one calendar year before the state’s next general congressional election, Gov. Phil Bryant would have to schedule a special election within 100 days of the vacancy – a quick turnaround, likely attracting candidates with existing campaign war chests and name identification.

But if Cochran’s seat becomes vacant after Nov. 6, Bryant would appoint a temporary senator who would serve until a special election on Nov. 6, 2018, the next congressional general election. Cochran’s current term ends in 2020, so any candidate who won a special election before then would serve the remainder of that term.

Cochran has served in Congress for 44 years. He was first elected to the House of Representatives in 1972. Then in 1978, he was elected to the Senate, and he has been re-elected six times. He is the third longest-serving current senator, behind Patrick Leahy of Vermont and Orrin Hatch of Utah.