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WASHINGTON — President Donald Trump should either delay his State of the Union address or submit it in writing, Speaker Nancy Pelosi wrote Wednesday in a letter citing the security burdens that the annual address to a joint session of Congress would place on a partially shuttered federal government.

"Sadly, given the security concerns and unless government re-opens this week, I suggest that we work together to determine another suitable date after government has re-opened for this address or for you to consider delivering your State of the Union address in writing to the Congress on January 29th," Pelosi wrote in the letter to Trump.

The White House did not immediately reply to NBC's requests for comment, but Pelosi told reporters later in the afternoon that she had not heard back from the president regarding her suggestion.

Parts of the federal government, including some operations of the Department of Homeland Security, have been closed down since Dec. 22, when the spending authority for several federal agencies lapsed amid an an impasse between Trump and Congress over his request for billions of dollars in funding for a border wall.

Homeland Security Secretary Kirstjen Nielsen said on Twitter Wednesday that her department is ready and prepared to provide security for the State of the Union.

The Department of Homeland Security and the US Secret Service are fully prepared to support and secure the State of the Union. We thank the Service for their mission focus and dedication and for all they do each day to secure our homeland. — Sec. Kirstjen Nielsen (@SecNielsen) January 16, 2019

A senior law enforcement official also told NBC News that the Secret Service, which is under DHS, is ready to offer protection during the State of the Union, should it move forward as scheduled.

"It's a no-fail mission," the official said.

Secret Service personnel are not being paid as a result of the shutdown, but its intelligence and protection functions are fully staffed.

"We've been planning for this for months, as we always do. It didn't start up 29 days ago," the official said.

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But a spokesman for Pelosi said later that her office was contacted by a furloughed DHS employee “who expressed serious concerns that the department has insufficient staffing levels to sufficiently manage the security needs for the upcoming State of the Union address due to furloughs of critical staff.”

Republicans, including House Minority Leader Kevin McCarthy, R-Calif., criticized the speaker for citing shutdown-related security concerns in a bid to move the State of the Union.

"It is not a security issue, that’s politics and you know it," McCarthy said. "For her to say security ... there is no security issue, it is pure politics and it’s wrong."

A State of the Union address has not been rescheduled since President Ronald Reagan chose to move his planned Jan. 28, 1986, speech when the Space Shuttle Challenger blew up that morning. Reagan instead addressed the nation from the Oval Office that night and postponed the State of the Union.

Asked if the letter meant the speaker was "disinviting" Trump, House Majority Leader Steny Hoyer, D-Md., at first said this was the case, telling NBC News Wednesday morning that the House is sending Trump a message that normal business won't be conducted while large parts of the government remain closed.

His office later said he had not read the full letter at the time he made the comments, and that he had mischaracterized its contents.

Pelosi herself told reporters she was not disinviting Trump.

"No, no, no. It's on the strength of the statement of the secretary of Homeland Security about all of the resources that are needed to prepare for a State of the Union Address, which she calls an 'event of special security,'" the speaker said.

Multiple sources said there was a walk-through scheduled at the U.S. Capitol today for all national security and governmental entities involved in a State of the Union address, but that planned meeting was "postponed at the request of the speaker's office."

There are typically several of these meetings leading up to the high profile address, and numerous agencies had been invited to take part.

Sources said the planned walk-through was scrapped after the speaker's letter to the president suggested his speech to Congress be rescheduled due to the shutdown. Sources said overall planning for the address has been in the works for months.

The speaker's office confirmed they requested today's meeting be postponed.

Pelosi's letter was sent one day after a group of moderate Democrats boycotted Trump's invitation to the White House for a lunch to discuss the border-wall fight at the heart of the shutdown.

On Wednesday, seven Democratic members of the bipartisan Problem Solvers Caucus — Reps. Josh Gottheimer of New Jersey, Thomas Suozzi, Anthony Brindisi and Max Rose of New York, Vicente Gonzalez of Texas, Dean Phillips of Minnesota, and Abigail Spanberger of Virginia — said they planned to meet with Trump at the White House.

"There is strong agreement across the aisle and around the country: We must reopen the government. Our security, safety, and economy have been compromised, and millions of families are suffering," they said in a statement. "There is also strong agreement that if we reopen the government, the possibility exists to work together and find common ground to tackle some of our country’s toughest problems and fix them. But that conversation can only begin in earnest once the government is reopened. We accepted the White House’s invitation to meet today to convey that message."

Afterward, White House Press Secretary Sarah Sanders tweeted that Trump "and his team had a constructive meeting" with the Problem Solvers Caucus members.

"They listened to one another and now both have a good understanding of what the other wants," she added. "We look forward to more conversations like this."

Meanwhile, a letter is circulating among a bipartisan group of senators that they plan to send to Trump calling on him to reopen the government.

“We respectfully request that you join us in supporting a short-term Continuing Resolution (CR) of three weeks to give Congress time to develop and vote on a bipartisan agreement that addresses your request. We commit to working to advance legislation that can pass the Senate with substantial bipartisan support," said the draft letter obtained by NBC News.