GOP leaders on Capitol Hill are scrambling to reach a deal with a bloc of 15 Senate Republicans threatening a government shutdown to force a fight over the Biden administration's vaccine mandates.

Why it matters: The push to defund the mandates — by holding the short-term government funding bill hostage — is largely symbolic, and highly controversial within the Republican Party. A shutdown as early as midnight Friday could trigger everything from national park closures to delays in receiving Social Security checks.

• Regardless of whether the group of conservatives backs off its threat, the trajectory is that a short-term funding bill ultimately will pass — and won’t “defund” vaccine mandates.

What we're hearing: According to several senators and their aides, the most-likely scenarios as Congress barrels toward its deadline at midnight Friday:

Option 1: At least one of the 15 senators — a group that includes Sens. Mike Lee (R-Utah), Ted Cruz (R-Texas), Roger Marshall (R-Kan.), Rick Scott (R-Fla.) and Ron Johnson (R-Wis.) — objects to a unanimous consent (UC) vote that would speed up passage of the short-term funding bill, triggering a shutdown.

• It would likely last only for the weekend, due to allotted time agreements for debating a bill, and a final vote would likely take place Sunday evening, leadership sources tell Axios.

Option 2: Senate leaders agree to hold a vote on an amendment defunding Biden's vaccine mandates. It fails, given Democrats would prevent it from receiving the necessary 51 votes to pass, but the exercise would give Republicans a chance to say they voted on it.

• This is only an option if all of the senators threatening a shutdown agree to it.

Option 3: Senate leaders reach a different agreement with the group that allows it to address its issues in another manner.

• As of now, no such deal seems imminent.

Between the lines: While all 50 Republican senators oppose the Biden administration vaccine mandates, most of them don't think risking a shutdown is the right way to eliminate them.

• “I don’t think shutdowns benefit people, like some folks think they do," said Sen. John Cornyn (R-Texas).
• “I just don’t quite understand the strategy or the play of leverage for a mandate that’s been stayed by 10 courts,” Sen. Kevin Cramer (R-N.D.) told Politico. “I want the vaccine mandates lifted, but I don’t think the [spending bill] is the tool to do it. For all practical purposes, the mandates weaken every single day.”