Meanwhile, the Republicans, as soon as they’ve lost power and its attendant responsibilities, will comfortably revert to scorched-earth opposition mode, firing up the negative partisanship machine that has served them so well in elections past. If the Democrats do have an agenda, but haven’t defined it well in the public’s mind before the election, then the Republicans will define it for them. And the Democrats won’t find that characterization flattering.

Democrats are rightly outraged by the Republican tax cut. But they should run in 2018 not merely on the fiscal recklessness and unfairness of the bill, but on an alternative use of $1.5 trillion. Promise to cancel the tax cut and spend every dollar on essential infrastructure, from old-fashioned stuff like repairing bridges to forward-looking projects like upgrading the electrical grid. Dare the president to veto the very thing he touted as making him different from traditional Republicans.

And do it now, before the president can argue that the Democrats are just obstructing the administration’s own, still vague infrastructure proposals.