Trump says 3rd term isn't a joke, despite term limit

Postmaster General Louis DeJoy, who attracted scrutiny in the months leading up to the 2020 presidential election over his handling of mail-in voting but later earned bipartisan support for his stewardship of the enormous federal postal agency, announced his resignation on Monday.

In a lengthy statement, DeJoy said he informed the Postal Service Board of Governors on Monday that this would be his last day, which comes a month after he told them of his intention to retire.

"I believe strongly that the organization is well positioned and capable of carrying forward and fully implementing the many strategies and initiatives that comprise our transformation and modernization, and I have been working closely with the Deputy Postmaster General to prepare for this transition," he said.

"While our management team and the men and women of the Postal Service have established the path toward financial sustainability and high operating performance -- and we have instituted enormous beneficial change to what had been an adrift and moribund organization -- much work remains that is necessary to sustain our positive trajectory," the statement continued.

Deputy Postmaster General Doug Tulino will assume his role until a permanent successor is named, and a search is already underway, DeJoy said.

A group of teachers unions and public school districts are asking a federal judge in Massachusetts to block the Trump administration from dismantling the Department of Education, according to a lawsuit filed on Monday.

The lawsuit argued that Trump -- who signed an executive order last week directing Education Secretary Linda McMahon to close the DOE -- lacks the authority to shutter a department that was created through an act of Congress.

The group of unions and school districts argued that the Trump administration’s actions -- both the executive order and plans to terminate half the department’s employees -- would "hobble" the Department of Education and prevent it from conducting its statutorily mandated duties.

The case was assigned to U.S. District Judge Myong Joun, a Biden appointee.

The lawsuit marks the second case that seeks to block the dismantling of the Department of Education. Earlier this month, a group of Democratic attorneys general filed a similar lawsuit to block the termination of thousands of DOE employees.

-ABC News' Peter Charalambous

President Donald Trump announced Dr. Susan Monarez as his new pick to head the U.S. Centers for Disease Control and Prevention. Monarez is currently the acting director of the agency.

"As an incredible mother and dedicated public servant, Dr. Monarez understands the importance of protecting our children, our communities, and our future. Americans have lost confidence in the CDC due to political bias and disastrous mismanagement," Trump said in the post.

He added that Monarez, if confirmed, will work with HHS Secretary Robert F. Kennedey, Jr., to "prioritize Accountability, High Standards, and Disease Prevention to finally address the Chronic Disease Epidemic and, MAKE AMERICA HEALTHY AGAIN!"

The announcement comes after the administration withdrew Trump's other pick, Dr. David Weldon, citing the fact that Weldon (a vaccine skeptic) did not have the votes needed to be confirmed.

-ABC News' Michelle Stoddart

Senate Democratic Leader Chuck Schumer urged Senate Majority Leader John Thune and Senate Republicans to work with Democrats in calling for a "full investigation" into why military operations were coordinated over Signal rather than over taxpayer-funded secure communications channels.

The comments came after The Atlantic reported its editor-in-chief Jeffrey Goldberg was inadvertently added to the chat discussing a U.S. attack on Houthis in Yemen. The White House said the messages appear to be authentic.

"Mr. President, this is one of the most stunning breaches of military intelligence I have read about in a very, very long time," Schumer said on the Senate floor.

"This kind of carelessness is how people get killed. It's how our enemies can take advantage of us. It's how our national security falls into danger," he added.

-ABC News' Isabella Murray