White House says some employees were fired by mistake

Hours after being narrowly confirmed by the Senate along party lines, Robert F. Kennedy Jr. was sworn in to serve as Trump's health and human services secretary.

Joining the ceremony at the White House was Trump, who called Kennedy a "friend" who will lead "historic reforms" in American health care.

"Immediately after Bobby is sworn in, I will be signing an executive order establishing the President's Commission to Make America Healthy Again," Trump said. "This groundbreaking commission will be charged with investigating what is causing the decades-long increase in chronic illness, reporting its findings and delivering an action plan to the American people."

A fourth federal judge on Thursday blocked President Donald Trump’s executive order ending birthright citizenship.

The ruling from U.S. District Judge Leo Sorokin in Massachusetts comes after three similar rulings by judges in New Hampshire, Seattle and Maryland.

"The plaintiffs are likely to succeed on the merits of their claims under the Citizenship Clause," Sorokin, an Obama appointee, said in his ruling. "They are likely to suffer irreparable harm in the absence of relief, the balance of harms tips overwhelmingly in their favor, and the public interest favors an injunction."

The two Massachusetts-based immigrant advocacy groups that filed the lawsuit last month argued that the principle of birthright citizenship is "enshrined in the Constitution" and that Trump does not have the authority to issue the order.

-ABC News' Peter Charalambous and Laura Romero

President Trump is continuing to discuss his conversations with Russia's Vladimir Putin and Ukraine's Volodymyr Zelenskyy.

Trump spoke with Putin first, which Zelenskyy said on Thursday was "not pleasant."

Trump defended the move as he took reporters' questions in the Oval Office.

"We had a good talk with President Putin. I had a good talk with President Zelenskyy. Very good talk. And somebody said, oh, I should have called Zelenskyy first. I don't think so," Trump said. "I mean, we have to find out whether or not Russia wants to make a deal. I know that Zelenskyy wants to make a deal because he told me that. But I now know that Russia wants to make a deal."

President Trump, who vowed on the campaign trail to immediately bring down prices for American families, acknowledged that there could be some financial pain associated with tariffs as he signed a memo initiating the process for potential reciprocal tariffs on some U.S. trading partners.

"Prices could go up somewhat short term, but prices will also go down," Trump said as he took questions in the Oval Office.

Trump repeated multiple times that the tariffs will result in job growth, telling reporters "the jobs will go up tremendously." He also argued that they will help American farmers and manufacturers.

"There could be some short-term disturbance, but long term, it's going to it's going to make our country a fortune," Trump said.