With 800,000 federal workers and unknown numbers of citizens suffering under the ongoing US government shutdown, the acrimony between President Donald Trump and Speaker of the House Nancy Pelosi was taken to a new level Thursday.

At odds over the president's insistence that Congress provide $5 billion in funds for his border wall before he agrees to reopen the government, Pelosi irked Trump on Tuesday by suggesting he delay his State of the Union (SOTU) address, scheduled to be delivered on January 29, due to lack of security funding.

The two agencies responsible for security at the event, the Secret Service and the Department of Homeland Security are directly affected by the shutdown. 

Allies of the president criticized the speaker's move as "politically motivated."

Shutdown politics

Washington had been waiting for a response from the president, and on Thursday it came.

Trump responded in a letter to Pelosi, informing her that she would not be allowed to use a government airplane for a scheduled trip to Afghanistan. The letter, which was tweeted by spokeswoman Sarah Huckabee Sanders, described the trip as a "public relations event" to "Brussels, Egypt and Afghanistan."

The step was highly unusual as trips to war zones are never divulged in advance.

Pelosi Chief of Staff Drew Hammill responded by clarifying the president's mischaracterization of the trip, tweeting: "The CODEL [Congressional Delegation] to Afghanistan included a required stop in Brussels for pilot rest. In Brussels, the delegation was scheduled to meet with top NATO commanders, US military leaders and key allies."  

Hammill noted that the trip to Afghanistan was to "express appreciation" to US troops and did not include any stops in Egypt. He also pointed out that the president had traveled to Iraq during the shutdown and that another delegation, including trade and economy officials, will be heading to Davos next week. 

Later on Thursday, Trump canceled his delegation's trip to Davos, according to a statement issued by Sanders.

Senator Lindsey Graham, often an ally of Trump, said of the feud, "One sophomoric response does not deserve another."

Graham called Pelosi's move on the State of the Union "blatantly political" but said, "President Trump denying Speaker Pelosi military travel to visit our troops in Afghanistan, our allies in Egypt and NATO is also inappropriate."