Sen. Thad Cochran (R-Miss.) has not cast a vote since mid-September because of health problems. (Rogelio V. Solis/AP)

Sen. Thad Cochran (R-Miss.) has indefinitely postponed a return to Washington because of health complications, narrowing the already slim GOP majority in the Senate ahead of crucial votes on the budget.

Cochran, 79, hasn’t voted in the Senate since mid-September because of health problems, but he was expected to be back on Capitol Hill this week. His office said Monday that he had developed a urinary tract infection and has again delayed his return.

“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,” Cochran’s office said. No timetable was given.

The Senate plans to vote this week on a budget resolution that would pave the way for a sweeping tax cut plan, and they need a majority of the Senate to support the plan for it to proceed to the next step.

Perhaps referencing the uncertainty facing the vote, President Trump on Monday said “We think we’re in good shape for the budget, we hope.”

Republicans control 52 of the 100 Senate seats, and losing Cochran’s vote means they can afford to lose the support of only one other GOP member if they still want to pass the budget resolution. If the House and Senate pass matching budget resolutions, it would then allow the Senate to approve tax-cut legislation with only a majority of votes instead of the 60 votes typically needed for a procedure vote on legislation.

No Senate Democrats are expected to support the budget resolution, which would allow Congress to later pass a bill that adds $1.5 trillion to the national debt over 10 years by cutting taxes.

Even though Republicans have a very small majority in the Senate, members appeared to be coalescing around their budget resolution over the weekend. Sen. Susan Collins (R-Maine), who has defied the White House before on key votes, said on ABC on Sunday that she would “likely” vote to support it.

Sen. Rand Paul (R-Ky.), who frequently opposes GOP budget resolutions because he argues that they don’t do enough to eliminate the deficit, golfed with President Trump on Sunday and praised the White House tax-cut effort. A Paul spokesman said Monday, though, that the senator “has not taken a definitive position.”

Not all GOP members, however, have signaled how they will vote. Sen. John McCain (R-Ariz.) has expressed support for simplifying the tax code, but he has also pushed for more military spending and could oppose the budget if he feels it doesn’t do enough to boost the Pentagon.

Sen. Bob Corker (R-Tenn.) voted for the budget resolution in a Senate Budget Committee vote, but he has recently gotten into a war of words with Trump, and Trump has said he doesn’t expect Corker to ultimately support the tax plan.

If the Senate passes its budget resolution this week, then House GOP leaders will have to decide whether to accept the Senate plan or force senators into a conference committee, where differences between the Senate resolution and a different measure that already passed the House must be reconciled.

Many conservatives believe the House budget resolution offers less flexibility for sweeping tax cuts than the Senate measure, and the White House is pushing hard for the House to accept the Senate’s language. But House leaders have signaled they will not simply accept a budget passed by the Senate and will demand the lengthier conference process to work out differences.