Consider the odd three-year legacy of a single top position in the Trump administration.
Early on, former Army Lt. Gen. Michael T. Flynn was sent packing as President Donald Trump's first national security adviser.
During his boss's 2016 campaign Flynn had retweeted bizarre conspiracy theories against the Democrats. This raised alarms, but, of course, not from the candidate's inner circle.
As the new national security adviser the following year, however, Flynn lied to the FBI inquiring about his contacts with Russia and later pleaded guilty to it despite apparent attempts by Trump to shield him.
So it lingers as a stain on the White House that Flynn has yet to be sentenced.
On Friday, his lawyers asked a judge to delay the proceeding again. The question has arisen whether he sidestepped a cooperation agreement with former special counsel Robert Mueller. So an Oval Office mantra of "case closed" doesn't work here. Flynn's aborted tenure was just a prelude to the trouble that has rocked the office he left behind.
Next up was H.R. McMaster, an Army lieutenant general and Iraq War veteran who served for a year. While seen by outsiders as a stable force on Trump's security team, the president by all accounts chafed at the length and depth of his Oval Office briefings, and he clashed with other Trump advisers.
Three months into the job in 2017, The New York Times reported that Trump described him privately as "a pain" and complained that he talked too much.
In February 2018, after a series of indictments against Russian cyber operatives, Trump went public with an oblique slam at McMaster, laced with short-hand references to unsupported conspiracy claims.
Trump tweeted: "General McMaster forgot to say that the results of the 2016 election were not impacted or changed by the Russians and that the only Collusion was between Russia and Crooked H, the DNC and the Dems. Remember the Dirty Dossier, Uranium, Speeches, Emails and the Podesta Company!"
McMaster clashed with Trump on other big matters, ABC News reported, by urging preservation of the since-ditched 2015 nuclear deal with Iran and by speaking more forcefully than Trump about domestic racial violence.
And after McMaster was ousted, Trump said "Nobody has been tougher on Russia than I have" but McMaster soon remarked that Russia has been increasingly aggressive and that "we have failed to impose sufficient costs" on President Vladimir Putin's regime.
When he was succeeded in April of last year by John Bolton, the former UN ambassador under President George W. Bush, some called him the "anti-McMaster" and a voice for neoconservative interventionism.
Now it looks like Bolton's turn to be sidelined in the Trump world.
Bolton's resistance to negotiations to get the U.S. out of Afghanistan has irritated Trump, according to senior White House officials quoted by The Washington Post. As a result, the National Security Council under Bolton has been kept out of strategy sessions on a subject would ordinarily involve its leader, it was reported.
Bolton and Trump have also put out differing messages on Iran and North Korea. Some have cast the situation as a behind-the-scenes battle between Bolton and the State Department under Secretary Mike Pompeo. Whatever the problem, the role of this office, like several others, has yet to stabilize under Trump.