President Trump, more isolated than at any point in his presidency, is scheduled to leave Washington at the end of this week for a holiday respite: two-plus weeks at his Florida resort, Mar-a-Lago. When he returns in January, he will be girding for what is likely to be the most difficult year yet of his tumultuous presidency.

His approval ratings aren’t much different than they were when he took office. His hardcore supporters haven’t budged. GOP elected officials remain hesitant to break with him. But his party took a beating in the midterm elections, and the legal process continues to move closer to him. Newly empowered House Democrats are preparing to challenge his authority with hearings and investigations.

Republican elected officials have stuck with him, mindful of his support among the GOP rank and file. But Senate Republicans last week joined with Democrats to deliver a pair of rebukes over the administration’s policy toward Saudi Arabia and the president’s unwillingness to condemn Crown Prince Mohammed bin Salman, whom the CIA concluded sanctioned the murder of journalist and Washington Post contributing columnist Jamal Khashoggi. Was that a one-off or cracks in the wall?

As the White House's high rate of turnover continues, The Post's Phillip Rucker examines what's important to President Trump when he's selecting his staff. (Jenny Starrs/The Washington Post)

Trump’s on-again, off-again search for a replacement for outgoing White House Chief of Staff John F. Kelly is symptomatic of his situation. In any presidency, the role of chief of staff is vital. For Trump, at this moment, it could be crucial. Yet potential contenders walked away from the job until the president tweeted on Friday afternoon that he was naming budget director Mick Mulvaney as his acting chief of staff, not his permanent one.

The announcement came hours after former New Jersey governor Chris Christie took himself out of contention for the post. Christie had spent more than an hour with the president on Thursday talking about the job. His decision to withdraw from consideration came at the end of a week that began when Nick Ayers, who serves as chief of staff to Vice President Pence and who was in line to succeed Kelly, suddenly backed out. Several names were floated but none came to fruition.

Christie and Trump have been friends for years, long before they became rivals for the GOP nomination in 2016. Christie assumed he would outlast Trump in that competition. When the opposite happened, he immediately endorsed Trump, who later asked him to head up transition planning. However, days after the election, Christie was summarily dismissed as transition director. Trump then asked Christie to consider other jobs in the administration. Christie rejected them. Recently, he was reported to be in the mix to succeed Jeff Sessions as attorney general, a job he would have liked but which went to former attorney general William P. Barr.

Christie has maintained a cordial and clear-eyed relationship with the president. Though he carries some political baggage from his time as governor, he had credentials that few of the others considered for the chief of staff position could offer — skills that Trump likely will need in the year ahead. Among them were executive experience, political experience, communications skills, independent political relationships and, above all, legal experience as a former U.S. attorney.

Christie apparently concluded this was no time to go inside the Trump administration and to work for a president who rarely takes the advice of his advisers and whose volatility and unpredictability could prove to be even more detrimental in the months ahead.

The decisions by Ayers, Christie and others underscore the precariousness of Trump’s position. At a time when he will need all the strength, wisdom, firepower and support directly around him, Trump presides over a White House that is thinning out rather than beefing up.

The White House Counsel’s Office is understaffed heading into a year that could bring multiple requests for documents from congressional committees and the possibility of impeachment proceedings, if what special counsel Robert S. Mueller III ultimately reports rises to that level. So far that is an open question. Others already have moved out of the White House to jobs on the Trump 2020 campaign or the private sector. More could follow in the months ahead.

Some loyalists remain. Among them are Kellyanne Conway, Sarah Sanders, and the president’s daughter Ivanka Trump and son-in-law Jared Kushner. But on the issue of fresh recruits, the question is: Who would want to come to work for a president at this moment, knowing that could result in sizable legal fees as a side benefit?

For Trump, a group of people he once counted as among his most trusted advisers has been turned into a weapon in the hands of prosecutors. Michael Cohen, Trump’s longtime fixer and lawyer who once said he would take a bullet for Trump, has turned. Last week Cohen was sentenced to three years in prison for his crimes. He told the court that he had done some of what he did, including lying to Congress, to hide the “dirty deeds” of Trump.

In an interview with ABC’s George Stephanopoulos, Cohen repeated what he said in court, that he had acted at Trump’s direction in paying off two women who alleged they had affairs with the president. He accused Trump of being a serial liar. Trump in turn has accused Cohen of lying, but the president’s credibility on these matters has been shredded. He first denied any knowledge of the payments to Karen McDougal and adult-film actress Stormy Daniels, but his story has changed repeatedly, whenever evidence comes forward that undermines what he last said.

Another person who once protected the president and is now on the other side is David Pecker, of American Media, the publisher of the National Enquirer, which shielded Trump through the campaign by buying and killing damaging stories and through phony stories about Hillary Clinton. On the day Cohen was sentenced, Pecker acknowledged in a filing that the Enquirer — out of concern that the revelation could influence the outcome of the election — had paid McDougal $150,000 to keep her story from becoming public.

Equally worrisome for Trump could be the role of Allen Weisselberg, the Trump Organization’s longtime chief financial officer and the person who must know as much as anyone about the inner financial workings of Trump’s empire. He has been granted immunity from prosecution in return for his cooperation.

Meanwhile, Trump’s former national security adviser, Michael Flynn, has pleaded guilty to lying to the FBI and has cooperated with prosecutors. His former campaign chairman, Paul Manafort, is in prison for crimes unrelated to the campaign. His former deputy campaign manager, Rick Gates, Manafort’s business partner, has also pleaded guilty for his role in the Manafort business.

No one outside Mueller’s circle knows what the final conclusions of his investigation will say — on Russia, on campaign finance violations, on the financial dealings of the Trump Organization, on any of the multiple threads that exist. The same can be said of the work of federal prosecutors in the Southern District of New York.

Congress is not likely to impeach the president over violations of campaign finance law, but the congressional machinery is cranking up to investigate the many aspects of Trump’s operations that have fallen under the view of prosecutors. The president can only wait, nervously, to see where it all leads. He will continue to fire back, to try to diminish the work of the prosecutors. But he does so from a far shakier position.