Unless Congress acts, the U.S. government will hit its $16.7 trillion borrowing limit by mid-October.

That’s the latest estimate from Treasury Secretary Jack Lew, delivered in a letter last week to House Speaker John Boehner, R-Ohio. Coupled with the Sept. 30 expiration of the government’s authority to spend money on discretionary programs, Lew’s letter sets the stage for yet another round of Washington’s seemingly endless partisan wrangling over fiscal policy.

To date, no combination of policy necessity and deadline pressure has sufficed to force a “grand bargain” that would address the country’s long-term budgetary imbalances.

In some ways, the impasse has worsened since Congress and President Obama cobbled together a temporary fix to the “fiscal cliff” drama nine months ago.

A promising series of meetings between Obama and a group of compromise-minded Republican senators fizzled. Sen. Ted Cruz of Texas and others on the GOP right launched a deeply mischievous campaign to “defund” Obamacare, the premise of which is that this is the last chance to stop the hated program and Republicans should reject any spending bill that contains money for it — even if that means shutting down the government.

Never mind a Congressional Research Service paper that shows this would be futile, since Obamacare’s implementation does not require new discretionary spending authority.

The defunders make it more difficult for Boehner and other party leaders to maintain unity in their ranks, the necessary precondition for even a short-term budget bill.

Still, the GOP has an overwhelming political interest in avoiding blame for a partial shutdown, so Boehner may be able to find the votes for a continuing resolution that keeps Washington operating for a couple of months, at or near current spending levels.

Boehner has provocatively forecast “a whale of a fight” over the debt limit, but assuming an extension can be arranged, that — plus a continuing resolution — would give Democrats and Republicans time to work on something a bit more permanent.