WASHINGTON — Chaos. Confusion. Confrontation.

The Trump administration and Congress are wrestling with serious challenges this Thursday before Christmas. President Donald Trump’s government-by-tweet and erratic tactics are keeping Congress in town with members struggling to keep government open with a Friday night funding deadline.

And in a dramatic wrap-up to his career in Congress, Rep. Luis Gutierrez, D-Ill., in one of his last acts as a member, called Department of Homeland Security Secretary Kirstjen Nielsen — and the Trump White House — liars at a hearing.

Chaos: Trump announced in a tweet the pullout of troops in Syria, a move made without the backing of top military brass or U.S. allies in the region. That triggered the Thursday resignation of Defense Secretary James Mattis, who, in a candid letter, outlined a series of differences he had with the president.

Mattis, concerned about Trump’s tilt toward Russia and China at the expense of U.S. allies, wrote, “I believe we must be resolute and unambiguous in our approach to those countries whose strategic interests are increasingly in tension with ours.”

Alluding to Trump’s shabby public treatment of the leaders of strong allies, the Pentagon chief said in his letter, “My views on treating allies with respect and also being clear-eyed about both malign actors and strategic competitors are strongly held and informed by over four decades of immersion in these issues.”

Rep. Brad Schneider, D-Ill., a member of the House Committee on Foreign Affairs, said in a statement, “We all share the desire to fully defeat ISIS, end the civil war in Syria and thwart Iran’s nefarious influence. Unfortunately, the President’s approach will more likely push each of these objectives further out of reach.”

Confusion: On Wednesday, congressional leaders thought they had a short-term deal with Trump to continue funding the federal government, kicking down the road Trump’s insistence on getting $5 billion for a southern border wall, the one Mexico was supposed to pay for.

With no deal by Friday night, a partial federal government shutdown kicks in.

Facing criticism from the Freedom Caucus GOP members and conservative media powers Laura Ingraham, Rush Limbaugh, Drudge and some of his friends at Fox, Trump changed his mind and walked away from the deal.

House Speaker Paul Ryan, R-Wis., at the White House said Trump won’t sign a short-term measure without his wall.

Rep. Bobby Rush, D-Ill., said in a statement, “House Republicans should not be allowed to hold our government hostage simply because they are afraid of what Fox News will say about their actions.”

BTW… A government shutdown will not impact Special Counsel Robert Mueller. His office confirmed on Thursday that it is “funded from a permanent indefinite appropriation and would be unaffected in the event of a shutdown.”

How will this end?

It’s a Trump reality show. No one knows.

Confrontation: Gutierrez, who has made immigration reform a centerpiece of his congressional career, used a Judiciary Committee oversight hearing to blister Nielsen, who he addressed with contempt.

The hearing with Nielsen was a last stand for Republicans, who lose control of the House on Jan. 3, when the newly empowered Democrats take over. On Thursday, it was still the GOP majority in charge.

“…I want to start by praising this administration and the role that it’s had because there’s one thing that this administration’s done better than any other administration in American history and that is lie,” Gutierrez said.

“…But I have to say the all-time record for lying in the face of all the evidence was a tweet you, madam secretary, sent out on June the 17th and it says, ‘We do not have a policy of separating families at the border.’

“…Shame on us for wearing our badge of Christianity during Christmas and allow the secretary to come here and lie.”

Nielsen said Gutierrez’s accusations were “fighting words.”

“I’m not a liar,” Nielsen said. She claimed that by her definition — which denies that children have been split from their families, which is a fact — “We’ve never had a policy for family separation. I’m happy to walk the gentleman through it again.”

Gutierrez didn’t want Nielsen’s lecture.

He walked out.

First elected in 1992, it was quite a final exit for Rep. Gutierrez.