Treasury Secretary Steven Mnuchin. (Susan Walsh/Associated Press)

THERE SEEM to be two kinds of Republicans: those who think that the full faith and credit of the United States can be the subject of political experimentation, and sensible ones.

Treasury Secretary Steven Mnuchin fits in the latter category. He has repeatedly called upon Congress, controlled by the GOP, to pass an increase in the statutory debt limit, with no policy strings attached, so that the United States government may continue borrowing past the current, already expired ceiling of $20 trillion — and pay all of its obligations on time. The stability of the financial system, domestic and international, depends on preserving the “risk-free” status of U.S. debt, earned over centuries. A failure to raise the debt limit would imperil this status, causing a “serious problem,” as Mr. Mnuchin has put it with considerable understatement.

Lawmakers have so far declined to follow his advice, however, thus violating Mr. Mnuchin’s recommendation, made six weeks ago, to take care of business before the August recess, which for the House began July 29. Mr. Mnuchin can continue to pay the federal government’s obligations by means of “extraordinary measures” through about mid-October, but he says the drop-dead date for legislative action is Sept. 29 — giving Congress just 12 working days after it returns from August recess.

Mr. Mnuchin is getting no help from Mick Mulvaney, the director of the Office of Management and Budget, who hails from the wing of the GOP that believes in playing political games with this issue. On Sunday, Mr. Mulvaney answered “yes” when CNN’s Jake Tapper asked if the White House policy was to insist Congress not vote on any other legislation, including the debt ceiling, before trying once again to repeal Obamacare. This appeared to reopen a rift with Mr. Mnuchin that first appeared in the spring, when Mr. Mulvaney spoke of making a debt-limit extension contingent on spending cuts — only to be publicly contradicted by Mr. Mnuchin, apparently with President Trump’s authorization.

Now, who knows? Certainly Mr. Mnuchin’s delicate talks with Republican and Democratic senators on a possible debt-limit deal haven’t gone anywhere, and probably won’t as long as neither side in the Senate knows exactly where the White House stands. “The Trump administration believes it’s important to raise the debt ceiling as soon as possible,” said Sarah Huckabee Sanders at her daily news briefing Tuesday — fine as far as it goes, but not quite an endorsement of unconditional debt-limit extension, which is Mr. Mnuchin’s position and the only responsible one.

Mr. Trump’s chief of staff, retired Marine Gen. John F. Kelly, got his new job with instructions to impose order on the chaos that reigns at 1600 Pennsylvania Avenue. We can’t think of a better place to start than by bringing everyone in the administration into line, starting with the man at the top, behind Mr. Mnuchin’s position on the debt ceiling. The hour is getting late, and the stakes are immense.