One of the most revealing things about American politics, and of the journalists who cover it for a living, is the unspoken assumption that Democrats will rescue Republicans, and thus the country, from the reckless way they have treated the statutory debt limit since 2011. If this assumption is correct (and it almost certainly is) then it demonstrates a profound asymmetry between the parties, as well as an awareness on the part of the political media, which often treats the two parties symmetrically, that something is dangerously dysfunctional about one of them.

This conventional wisdom, which I mostly share, will be tested in September, when Congress has to increase the debt limit or plunge the country into an economic crisis.

Though Republicans control the House of Representatives and the Senate, many of them will refuse to increase the debt limit without accompanying policy ransoms, meaning Democrats will be expected to provide the decisive votes. And this is the best-case scenario. Until recently, cabinet officials in Donald Trump’s administration disagreed with one another over whether the president should side with the hostage-takers or the more responsible faction. They are fortunately all on the same page now—

WH budget chief Mulvaney says he & entire administration now on board behind "clean" debt limit increase - no longer seeking spending cuts — John Harwood (@JohnJHarwood) August 3, 2017

—but we can’t dismiss the possibility that Trump will do something erratic, like refuse to sign any bills until Republicans pass a health care repeal bill. Democrats, in other words, might have to vote not in modest numbers, but in overwhelming ones, to make a clean debt limit increase veto-proof.

In either case, though, I’d like to challenge the unstated supposition that Democrats will and should provide these votes without reciprocation. It would be hypocritical and destabilizing for Democrats to demand policy concessions from Republicans in exchange for their votes, but that doesn’t mean Democrats have to play themselves by voting for whatever kind of debt limit increase Republicans propose.