He's consistently shifted his position on immigration, so much so that a bipartisan deal fell through just in time for frustrated Democrats to threaten to vote against a spending bill.

He cast doubt on whether he'd sign a short-term spending bill to keep the government's lights on for another month, hours after his spokeswoman said he would.

A shutdown “could happen,” President Trump told Reuters in an interview Wednesday.

And hours before a precarious vote in the House of Representatives to avoid such a scenario, Trump pulled the rug out from under GOP leaders by seeming to take away their only leverage to get Democrats on board: funding the Children's Health Insurance Program, which Congress let expire in September, at the same time. (House Speaker Paul D. Ryan later said that's not what Trump meant.)

In short, Trump has done pretty much everything he can to increase the chances of a government shutdown. It's almost as if he wants one.

“We don’t have a reliable partner at the White House to negotiate with,” Sen. Lindsey O. Graham (R-S.C.) told The Post's Ed O'Keefe on Thursday morning, as he walked to the Capitol. "This has turned into an s-show for no good reason and the only way out of this thing is to grow up a little bit — and I think that’s going to happen.”

“Oh my — that’s what I’m talking about,” Rep. Mark Sanford (R-S.C.) said to O'Keefe when told about Trump's recent shutdown tweets. “It’s fluid, topsy-turvy, whichever you prefer.”

“That’s just another one of those inexplicable tweets that’s not very helpful,” Rep. Charlie Dent (R-Pa.) told O'Keefe.

Whether it's because Trump doesn't know what he wants, doesn't have a grasp on the issues or honestly doesn't mind a government shutdown is up for debate. (None of those is mutually exclusive, by the way.)

But the effect of Trump's indecision and lack of expertise is the same. He is getting in the way of Congress doing its job. Not that Congress has it all figured out. A day ago, House GOP leaders were throwing in last-minute goodies for both sides just to get a majority to vote for a bill that funds the government for another month.

But Trump getting in the way of Congress is nothing new. He has an uncanny ability to disrupt Congress at the exact worst moment for GOP leaders.

Last year the House of Representatives passed a sanctuary cities bill that shifted the tide in Trump's battle with liberal cities and states. But it was entirely overshadowed by Trump attacking “Morning Joe” co-host Mika Brzezinski for an alleged facelift.

In December, on the day Senate Republicans secured enough votes to rewrite the tax code for the first time in three decades, Trump's former national security adviser Michael Flynn pleaded guilty to lying to the FBI about his conversations with the Russian ambassador.

And just last week, he tweeted his opposition to a surveillance program that his own administration said he supported. Republican leaders almost scrapped a vote to reauthorize the program, White House chief of staff John F. Kelly had to rush to the Capitol for damage control, and Trump corrected himself on Twitter to say he supported the bill.

No one really knows why Trump insists on getting in the way of Congress. The surveillance bill tweet seemed to come about because Trump was parroting what he heard on Fox News that morning and didn't understand the difference between a foreign surveillance bill and a domestic one.

Democrats who want a spending bill that also protects young immigrants in the country illegally were repelled by Trump describing Haiti and African nations as “shithole countries.” Trump has yet to explain why he just undercut House Republicans on children's health funding as leverage to avoid a shutdown.

That's another reason Trump is so frustrating for members of Congress. About the only predictable thing about the president is he's going to find some way to muck up negotiations, right when Congress can least afford it.