The surest way to guard our democracy against foreign interference? Persuade the meddlers not to meddle in the first place. Congress has a last chance to take a common-sense step in that direction before lawmakers call it a year.

Sen. Chris Van Hollen, D-Md., has written a letter exhorting Majority Leader Mitch McConnell, R-Ky., to support a provision in this year's National Defense Authorization Act (NDAA) that would trigger cross-sector sanctions on any government that tried to tamper with U.S. elections. The measure mirrors the Deter Act that Sen. Marco Rubio, R-Fla., first introduced with Van Hollen almost two years ago. The Senate has passed by voice vote a resolution instructing the conferees currently finalizing the authorization act to take similar steps, and the House has approved a sister amendment.

That leaves Van Hollen with a question for McConnell: "Why are you blocking this measure in the NDAA conference?"

We're wondering the same thing -- not only of the majority leader but also of the Republican committee chairmen who reportedly have their own concerns with the bill. These qualms likely have something to do with policy, process and politics all at once. Some may prefer, for example, for sanctions this far-reaching to occur at the president's discretion. The trouble is, this president has displayed more interest in palling around with Vladimir Putin than in holding him to account. Others may protest that an ambitious bill such as this one should be debated and marked up under regular order. But that's less convincing an argument when legislation that runs the election security gamut has been prevented from making it to the floor at all.

That leaves politics. Republicans who chafe at what they see as Democrats' one-sided attempt to ram through a no-compromise provision should come to the table with any legitimate concerns about the bill's language and how it might be improved. But the measure's basic premise ought to be a no-brainer: Russia meddled in our elections. Russia wants to meddle again. The Kremlin certainly will mount a repeat offensive if we don't give it a reason not to. Other nations wavering on whether to try their own hand at interference also learn the wrong lesson from an anemic U.S. response.

Republicans are right that this issue shouldn't be partisan. All the more reason for them to get on board and go home for the holidays without giving Russia a gift.