WASHINGTON -- The president tweeted Wednesday morning that he wished he had picked someone other than Jeff Sessions as his attorney general. He cited Republican Rep. Trey Gowdy's comments on "CBS This Morning."

"If I were the president and I picked someone to be the country's chief law enforcement officer, and they told me later, 'Oh, by the way I'm not going to be able to participate in the most important case in the office,' I would be frustrated too," Gowdy said.

CBS News has learned that special counsel Robert Mueller is increasingly focused on the president's interactions with the attorney general as part of his investigation into possible obstruction of justice.

On Wednesday, White House Press Secretary Sarah Sanders refused to say why the president hasn't followed through on his threats.

"Look, the president has made his viewpoint very clearly known, and I don't have any personnel announcements at this point," Sanders said.

Sessions recused himself from the Russia probe in March 2017. Since then, the president has repeatedly insulted him as "disgraceful," "weak," and "beleaguered."

Sessions has given no indication he intends to resign and defended his recusal in March.

White House advisers are concerned that firing Sessions could cost the president support among core supporters and members of Congress who support Sessions, especially his tough stance on immigration. Sessions will spend most of the next month touring the country in support of those more aggressive immigration policies.

Late Wednesday night, the president weighed in on Sessions again, on Twitter: