He's finally been convinced that Whitaker simply will not fly

His very successful administration.

P.S.  I have to assume that William Barr, who also served as George HW Bush's AG, is not an honorable person or he would not accept the nomination.  I also have to assume that somebody finally got through to His Lardship that it would be hugely embarrassing for him if Whitaker went before Congress for confirmation, not to mention dangerous for Whitaker.

Barr, too, has a paper trail featuring Trump-friendly commentary on the [Mueller investigaion] matter, and the New York Times has reported that Trump has pressed Barr on whether he would recuse himself (long the source of Trump’s Jeff Sessions-related angst). At the least, Trump seems to want Barr to guide the investigation in a new direction.

[...]

[Barr's] past may carry clues, including some pretty striking parallels involving another special counsel investigation.

It was the early 1990s, and special counsel Lawrence Walsh’s investigation of the Reagan-era Iran-contra scandal had been dragging on far longer and penetrating much deeper than the George H.W. Bush administration liked. Barr, then serving as Bush’s attorney general, was perturbed, too.

So much so, in fact, that he regularly considered firing the special counsel, according to The Washington Post’s Bob Woodward in 1999.

  WaPo

Music to Trump's ears. And he must be assuming Congress won't dare reject Barr after the week's worth of praise for George HW Bush.

This scene comes from November 1992, just after Bush lost his reelection race. Reagan’s defense secretary, Caspar W. Weinberger, had been indicted four days before the election.

[...]

As he walked into the White House, [Bush] spotted Attorney General William Barr in the crowd. With an index finger motion of “follow me,” the president summoned Barr to the Oval Office. When they were alone, Bush exploded about the Weinberger re-indictment. “It appears this was very political!” he bellowed, following up with a string of very pungent remarks. “Cost me the election,” he said furiously.

Barr said he thought the re-indictment was a crude political act with a political motive. Career Justice Department prosecutors would never bring out controversial information in an indictment just before an election. Barr said he wanted to dismiss Walsh. He knew the law well. He could remove Walsh for “misconduct.”

"Walsh has abused his power!" Bush said, inviting the attorney general to fire Walsh.

[...]

He said he had asked himself, "What is the standard that applies to this guy?"

He had consulted his most trusted and confidential advisers in the department. They worried that if Barr terminated Walsh, there would be a new firestorm. Because Walsh was appointed under the independent counsel law, Barr said, the courts would replace him with another person. The investigation would continue.

Neither man had to mention the obvious alternative: a presidential pardon for Weinberger.

And that’s what eventually happened. The charges against Weinberger were expanded in late December 1992, leading Bush to pardon him and five others on Christmas Eve. The move essentially took the legs out from beneath Walsh’s investigation without removing him.

[...]

Barr made little secret what he thought of Walsh’s tenure as special counsel in the years that followed.

“It was very difficult because of the constant pendency of the Iran-contra case and Lawrence Walsh, who I thought was a — I don’t know what to say in polite company,” Barr said in 2001.

[...]

[T]here are key parallels, including an administration that thinks a special counsel has gone beyond its bounds, the apparent possibility of pardons as a workaround and regular consideration of firing the special counsel to end it all (which Trump has reportedly attempted twice).

[...]

Barr may not regard Mueller as being as out of control as he thought Walsh was, but he has criticized political donations made by Mueller’s prosecutors. He has also suggested that the evidence for investigating potential Trump campaign collusion with Russia wasn’t as strong as it was for investigating Hillary Clinton on Uranium One, a deal approved when she was secretary of state.

...but hey, do what you want...you will anyway.