She imperiled his State of the Union address. He denied her a plane to visit troops abroad.  The shutdown battle between President Donald Trump and House Speaker Nancy Pelosi is playing out as a surreal game of constitutional brinkmanship, with both flexing political powers from opposite ends of Pennsylvania Avenue as the negotiations to end the monthlong partial government shutdown remain stalled.

In dramatic fashion, Trump issued a letter to Pelosi on Thursday, just before she and other lawmakers were set to depart on the previously undisclosed trip to Afghanistan and Brussels. Trump belittled the trip as a “public relations event” — even though he had just made a similar warzone stop — 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, who had been smarting since Pelosi, the day before, called on him to postpone his Jan. 29 State of the Union address due to the shutdown.

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. Lawmakers were caught off guard. A bus to ferry the legislators to their departure idled outside the Capitol on Thursday afternoon.

The political tit-for-tat between Trump and Pelosi laid bare how the government-wide crisis has devolved into an intensely pointed clash between two leaders determined to prevail. It took place as hundreds of thousands of federal workers go without pay and Washington’s routine protocols — a president’s speech to Congress, a lawmaker’s official trip — became collateral damage.

Pelosi spokesman Drew Hammill said the speaker planned to travel to Afghanistan and Brussels to thank service members and obtain briefings on national security and intelligence “from those on the front lines.” He noted Trump had traveled to Iraq during the shutdown, which began Dec. 22, and said a Republican-led congressional trip also had taken place.

Trump’s move was the latest example of his extraordinary willingness to tether U.S. government resources to his political needs. He has publicly urged the Justice Department to investigate political opponents and threatened to cut disaster aid to Puerto Rico amid a spat with the island territory’s leaders.

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.”

While there were few signs of progress Thursday, Vice President Mike Pence and senior adviser Jared Kushner dashed to the Capitol late in the day for a meeting with Republican Senate Majority Leader Mitch McConnell. And the State Department instructed all U.S. diplomats in Washington and elsewhere to return to work next week with pay, saying it had found money for their salaries at least temporarily.

For security reasons, Pelosi would normally make such a trip on a military aircraft supplied by the Pentagon. According to a defense official, Pelosi did request Defense Department support for overseas travel and it was initially approved. The official wasn’t authorized to speak by name about the matter, so spoke on condition of anonymity.

Federal authorities have arrested a man in Georgia who they are accusing of plotting to attack several prominent locations in Washington, D.C., including the White House.

Hasher Jallal Taheb had been under investigation by the FBI as part of a sting operation after local authorities reported concerns about him becoming radicalized last March, according to a criminal complaint filed in the federal court in the Northern District of Georgia in Atlanta on Wednesday.

A member of the community had reported to local law enforcement that Taheb had “become radicalized, changed his name and made plans to travel abroad,” the complaint states.

Taheb applied for a U.S. passport in July, stating that he had misplaced his previous one, and in August he put his vehicle up for sale, telling an FBI informant who expressed interest in buying it that he was selling the car to fund his travel overseas, according to the complaint.

Taheb told the FBI informant in October during a meeting in Cumming, Georgia, that he “wished to conduct an attack in the United States against targets such as the White House and the Statue of Liberty,” the document states. Taheb allegedly told the informant that “jihad was the best deed in Islam and the peak of Islam,” adding that “it was not complicated at all to do jihad today,” according to the complaint.

In a meeting with the informant and an undercover FBI agent on Dec. 2, Taheb allegedly stated that “they could do more damage” in the U.S. because abroad they would be “one of many.” He also allegedly said that he wanted to be a “martyr” and cause as much damage as possible, the complaint states.

On Dec. 7, Taheb allegedly showed the undercover operative a hand-drawn diagram of the White House’s West Wing in a composition notebook and asked for help with obtaining weapons and explosives for the attack, the complaint states.  “He said the group would fight to the end and make it a big bang,” according to the document.

Two days later, Taheb allegedly asked the undercover agent via text how “grocery shopping” was and offered to go with him to purchase the weapons and explosives, the complaint states.

On Dec. 14, Taheb allegedly “broadened his prospective targets,” indicating that he wished to attack the Washington Monument, the Lincoln Memorial and a “specific synagogue” in the Washington, D.C. area, which was not named, according to the complaint. He also discussed the need for a “base” where they could regroup and “give a speech to motivate people” and show clips of “oppressed Muslims,” the document states.

The next day, he allegedly uploaded a 40-page manifesto he authored to Google Docs, which stated the importance of “defensive jihad” and included justifications for “creating and leading his group to conduct violent attacks,” according to the complaint. He also created a group chat with the informant and undercover agent, where he would allegedly discuss his plans to attack in the following weeks.

Taheb allegedly met with the undercover agent on Jan. 9 and provided him with two backpacks, stating that he wanted to obtain the weapons within the next week and travel to Washington, D.C., the complaint states. Taheb allegedly told the undercover agent that the explosives would be inside the backpacks and would be detonated with cell phones.

On Saturday, Taheb allegedly met with the FBI informant, providing him with a camera, an American flag and an Israeli flag and stating that he wanted to conduct the attack on Thursday, according to the sworn affidavit.