Gosh, I hope they do it. It’d be a fascinating test of shutdown politics early in Trump’s presidency to see which side bears the brunt of the political fallout.

“We believe it would be inappropriate to insist on the inclusion of (wall) funding in a must-pass appropriations bill that is needed for the Republican majority in control of the Congress to avert a government shutdown so early in President Trump’s administration,” said the letter, which was provided to The Associated Press. Trump’s proposal for the wall was a centerpiece of his presidential campaign and he claimed he could persuade Mexico to pay for it.

The letter from Democrats implicitly threatens a filibuster showdown — and potential government shutdown — if Republicans try to attach controversial Trump agenda items to the must-do legislation…

While the letter says it would be “inappropriate” to include money for the border wall, it says Democrats would “strongly oppose” other provisions, including moves against Wall Street regulations or even an attempt to “defund” Planned Parenthood. Schumer demurred when asked last week whether he would lead a filibuster over money for the wall, but Monday’s letter appears intended to show that Democrats are unified against the idea. Trump also is preparing a request for additional border control and immigration agents.

The government is funded through April 28. If the new appropriations bill doesn’t pass by then, everything goes dark — and by “everything,” I mean some small sliver of federal services that would actually be affected by a temporary cut-off in funding.

The last time there was a shutdown, in 2013, it was Republicans who took more of the blame in public opinion polls — but that comes with caveats. Caveat one: The most outspoken senators blocking funding four years ago were GOPers like Ted Cruz and Mike Lee, who were trying to force the administration to delay the implementation of ObamaCare. It’s understandable that the public might have thought of them when assigning blame. The most outspoken senators this time will be Chuck Schumer, Elizabeth Warren, and Bernie Sanders. What’ll that do to the polling? Caveat two: The hit Republicans took in 2013 over the shutdown left barely a dent on the party, as it was just one year later that the GOP swept back into power in the Senate. That result was the inspiration for the new Democratic strategy of opposing Trump at every turn. Obstruction, up to and including a government shutdown, worked for Mitch McConnell. Now, supposedly, it’s going to work for the left too. We’ll find out in six weeks if Chuck Schumer really believes that.

It may be that the GOP would have suffered lasting damage from the 2013 shutdown if not for the fact that the disastrous rollout of ObamaCare interceded and refocused voters’ irritation towards the White House. It may also be that Republicans are forever destined to bear more blame in a shutdown because the public knows them as an anti-government party and simply assumes that, whenever the government stops operating, they must be behind it. That’s what makes Schumer’s threat here so fascinating: If he follows through, we’ll get a hard test of how much the politics of shutdowns are set in cement and how much are variable depending upon which party’s in the minority. There are X factors that will make the standoff more interesting than it might have been, too. One, of course, is Trump himself, who’d be on TV every day accusing Schumer of turning off the lights on vulnerable people who depend on federal assistance. That might have been a tough message to sell with a tea partier like Ted Cruz in the White House; with a big-government Republican like Trump, it’ll be easier. If he can convince the public that Democrats bear the blame for the shutdown, that could hurt the left in the midterms.

The other X factor cuts the other way, though — namely, the border wall doesn’t poll well:

That’s from a Quinnipiac poll taken in February but other polls taken over a span of months show similarly dismal numbers. Would the public support a shutdown to block a policy it dislikes, or would they punish a party that engineers a shutdown for its tactics regardless of the underlying policy? That’s another question a Schumer shutdown might help answer.

By the way, if you’re wondering why the Senate needs to appropriate funds for the wall, it’s because the amount of money that’s been appropriated in the past was, er, a little less than the White House was counting on. Here’s Mitch McConnell being asked last week if he thinks Mexico will end up paying for the project and answering … pretty bluntly.