This post has been updated with House Speaker Paul D. Ryan's (R-Wis.) comments. 

He's indecisive; he's extremely unclear on the issues and the language that lawmakers use to describe them; and when he does make up his mind, he's likely to change it the next day, or sometimes just a few seconds later.

Worse: In the middle of routine negotiations, he'll say something that shows his lack of understanding on the issues and then cause an international incident, as when he asked members of Congress on Thursday why the United States has to let in immigrants from “shithole countries” like Haiti and El Salvador and African nations.

President Trump, in other words, is not a reliable or knowledgeable negotiator. And, as a result, he has become close to impossible for his allies to work with and defend. This isn't a new revelation about the president, but Trump proved it true in spades this week, raising a very problematic question for members of Congress: How can it do its job with a president who is constantly undermining them?

If you're a member of Congress, for example, how do you plow forward on a deal to protect “dreamers” when you're instead forced to talk about what you think of the president describing majority-black and Hispanic nations as “shithole countries?

The answer seems to be that you don't. Whatever immigration deal Congress may have been inching toward less than 12 hours ago seems very much shattered. “This is like throwing gasoline to the fire,” said Rep. Adriano Espaillat (D-N.Y.), an immigrant from the Dominican Republic, told my Post colleagues, indicating just how willing already-skeptical Democrats are to negotiate with Trump.

Republicans in Congress demanded explanations, too. (After nearly 24 hours of silence, House Speaker Paul D. Ryan (R-Wis.) said this in Wisconsin: "First thing that came to my mind is, ‘Very unfortunate. Unhelpful.’")

Meanwhile, Trump was up early Friday morning muddying the waters on what he said.

Just 24 hours earlier, House Republicans nearly had to scrap a vote to reauthorize a surveillance law because the president tweeted something he appeared to have heard on Fox News about how the law might be harmful to him — even though his own White House had signaled its approval the night before.

As my Post colleagues report, that one tweet sent off a scramble at the highest levels in Washington:

House Speaker Paul D. Ryan (R-Wis.) spent 30 minutes on the phone with the president explaining the differences between domestic and foreign surveillance, as many fellow Republicans reacted in disbelief and befuddlement. White House Chief of Staff John F. Kelly also directly intervened with Trump, reiterating the program’s importance before traveling to the Capitol, where he parried questions from confused lawmaker.

And in a meeting with lawmakers Tuesday, Trump very nearly agreed with Democrats on basically everything to do with immigration — until House Majority Leader Kevin McCarthy (R-Calif.) interjected to correct him. In the end, Trump said he'd sign whatever Congress came up with, which was the opposite of the objective of the meeting: to get clarity on where the president stands.

This is a political headache for Republicans, who by now are used to spending their days being asked about Trump's latest controversy instead of their latest achievement. In fact, Trump has an uncanny knack for creating controversy right as Republicans score a policy victory.

But this week is more than bad politics. The shallowness of Trump's apparent understanding, and the extent of his biases, are coming more clearly to the public eye at a time when Congress has serious, intractable problems it needs to deal with.

The government needs to be funded by next week or it could shut down. Tens of thousands of young immigrants in the country illegally could lose their protections. A children's health-insurance program that millions rely on is going bankrupt. The CIA says it desperately needs Congress to reauthorize a foreign surveillance tool to fight terrorism. And disaster ravaged communities need billions of federal dollars to get back on their feet.

Meanwhile, in the first weeks of 2018, Trump is reaffirming a lesson Congress learned in 2017: If you want to get anything done, better to work around the president than with him. (And hope he doesn't say or tweet anything that could cause an international incident in the meantime.)

Downplaying and even ignoring the president. That's an extraordinary position for Congress to be in. But if there's a lesson to take from this week, it's that to be productive, Congress might have to do just that.