WASHINGTON >> President Donald Trump said he’ll be making a “major announcement” on the government shutdown and the southern border on Saturday afternoon as the standstill over his border wall continues into its fifth week.

The White House declined to provide details late today about what the president would be announcing. But Trump was not expected to sign the national emergency declaration he’s been threatening as an option to circumvent Congress, according to two people familiar with the planning.

Instead, Trump was expected to propose the outlines of a new deal that the administration believes could potentially pave the way to an end to the shutdown, according to one of the people. They were not authorized to discuss the announcement and spoke on condition of anonymity.

The move — on Day 28 of a shutdown that has left hundreds of thousands of federal workers without paychecks — represents the first major overture by the president since Jan. 8, when he delivered an Oval Office address making the public case for his border wall. The president and his aides have said he will not budge on his demand for $5.7 billion in funding. Democrats have panned the number and said they will not negotiate until the government reopens, raising questions about how Trump might move the ball forward.

In a video posted on his Twitter feed late today, Trump said both sides should “take the politics out of it” and “get to work” to “make a deal.” But he also repeated his warnings, saying: “We have to secure our southern border. If we don’t do that, we’re a very, very sad and foolish lot.”

White House spokeswoman Sarah Huckabee Sanders said only that Trump was “going to continue fighting for border security” and “going to continue looking for the solution” to end what the administration had repeatedly referred to as a “humanitarian and national security crisis at the border.”

While few would argue that a humanitarian crisis is unfolding at the U.S.-Mexico border, as the demand for entry by migrants and the Trump administration’s hardline response overwhelm border resources, critics say Trump has dramatically exaggerated the security risks and argue that a wall would do little to solve existing problems.

Trump will be speaking from the Diplomatic Room at 3 p.m.

Trump’s evening tweet announcement came after House Speaker Nancy Pelosi today canceled her plans to travel by commercial plane to visit U.S. troops in Afghanistan, saying Trump had caused a security risk by talking about the trip. The White House said there was no such leak.

It was the latest turn — and potentially the most dangerous — in the high-stakes brinkmanship between Trump and Pelosi that has been playing out against the stalled negotiations over how to end the partial government shutdown.

And it showed once again the willingness of the former hard-charging businessman to hit hard when challenged, as he was earlier this week when Pelosi suggested postponing his State of the Union address until after the shutdown.

Julian Zelizer, a professor of history and public affairs at Princeton University, said the back-and-forth “gives new meaning” to tensions between the executive and legislative branches.

“There are public back and forths,” he said, citing relations between past presidents and House speakers. “But this kind of tensions, preventing the speaker from visiting the troops and the speaker suggesting the White House leaked information about a crucial flight, this is one more example of where Trumpism brings us into new territory.”

The political stakes are high as the shutdown moves into a fifth week, with hundreds of thousands of federal workers going without pay and no outward signs of resolution.

Sanders today stressed the importance of a looming Tuesday deadline to process paychecks, when the government will need to decide if workers get another round of zeros today’s payday.

“One of the key reasons that the president did not want Speaker Pelosi to leave the country is because, if she did, it would all but guarantee the fact that the negotiations couldn’t take place over the weekend,” Sanders told reporters.

It was an unusually combative week between the executive and legislative branches.

Tensions flared when Pelosi suggested Trump postpone the annual State of the Union address, a grand Washington tradition — and a platform for his border wall fight with Democrats — that was tentatively scheduled for Jan. 29.

Trump never responded directly. Instead, he abruptly canceled Pelosi’s military flight on Thursday, hours before she and a congressional delegation were to depart for Afghanistan on the previously undisclosed visit to U.S. troops.

Trump belittled the trip as a “public relations event” — even though he had just made a similar stop in a conflict zone during the shutdown — and said it would be best if Pelosi remained in Washington to negotiate to reopen the government.

“Obviously, if you would like to make your journey by flying commercial, that would certainly be your prerogative,” wrote Trump.

Pelosi, undeterred, quietly began making her own preparations for the overseas trip.

But today, Pelosi said her plan to travel by commercial plane had been “leaked” by the White House.

“The administration leaked that we were traveling commercially,” Pelosi told reporters at the Capitol. She said it was “very irresponsible on the part of the president.”

She said the State Department told her “the president outing” the original trip made the scene on the ground in Afghanistan “more dangerous because it’s a signal to the bad actors that we’re coming.”

The White House said it had leaked nothing that would cause a security risk.

Trump’s trip to Iraq after Christmas was not disclosed in advance for security reasons.

Denying military aircraft to a senior lawmaker — let alone the speaker, who is second in line to the presidency after the vice president, traveling to a combat region — is very rare.

Democratic Rep. Adam Schiff of California slammed Trump for revealing the closely held travel plan, calling it “completely and utterly irresponsible in every way.”

Some Republicans expressed frustration. Sen. Lindsey Graham tweeted, “One sophomoric response does not deserve another.” He called Pelosi’s State of the Union move “very irresponsible and blatantly political” but said Trump’s reaction was “also inappropriate.”

The White House also canceled plans for a presidential delegation to travel to an economic forum in Switzerland next week, citing the shutdown. And it said future congressional trips would be postponed until the shutdown is resolved, though it was not immediately clear if any such travel — which often is not disclosed in advance — was coming up.