Trump is implying that McCabe, who helped oversee the 2016 investigation into Hillary Clinton's private email server, was biased in her favour because "Clinton puppets" gave money to his wife's political campaign.
McCabe's wife Jill did receive $700,000 in donations from the political action committee of Virginia's governor, who is a longtime Clinton supporter, and the Virginia Democratic Party when she ran for the state's Senate.
In other words, while Jill McCabe was a Senate candidate for the Democrats in Virginia, she received donations from Democrats in Virginia. She eventually lost the election.
Those donations were made before McCabe had any role supervising the Clinton email investigation. However, this week he did face questions from two congressional committees, which are investigating the FBI's handling of the Clinton email controversy.
Republicans argue he could not have been impartial in the Clinton investigation and should now be fired. Trump seems to share that view.
One of Trump's tweets, quoting Fox News commentator Ed Henry, asserted that McCabe was using his official FBI email account to promote his wife's campaign. It is unclear where that particular allegation originally came from.
The president's verbal assault on McCabe prompted a backlash from several prominent figures, with former CIA director John Brennan suggesting Trump "fears" the FBI and former Republican Congressman Joe Walsh saying his words would "bite him in the ass".
Trump has also spent the pre-Christmas period venting about the media's failure to sufficiently praise his achievements, particularly the tax reform bill that passed last week.
That last one shows a smear of blood, labelled CNN, on the bottom of Trump's shoe.
If Trump's insider polls are as strong as he claims, they would certainly fly in the face of public polling, which shows his approval rating hovering around 37 per cent and his disapproval at about 57 per cent.
However the tax reform bill is undeniably a major achievement for Trump as he finishes his first year in office.
It represents a sweeping, trillion overhaul of the tax code, impacting every corner of the economy through dramatic cuts to taxes for corporations and temporary reductions for individuals.
"As you know, $3.2 trillion in tax cuts for American families," Trump said when he signed the bill, shortly before leaving for his Mar-a-Lago holiday. "And they're going to start to see that because we're signing today."
He added that "we're going to bring back probably $4 trillion from overseas," and said corporations "are literally going wild over" the prospect.
"This is something that Republicans wanted for years and Democrats wanted for years and yet it never got done. Now it's being done."
Democrats have branded the tax plan a giveaway to the wealthiest that risks blowing a hole in the national debt, and polls have shown a majority of Americans oppose the reform.
But House Speaker Paul Ryan thinks they will be won over once they start to reap the benefits.
"The biggest tax reform in a generation is now the law of the land," he said after Mr Trump's signing. "As promised, the American people will begin the new year with a new tax code."
Trump believes he has achieved more during his first year than any of his predecessors. "We have more legislative victories than any other president," he said. Trump has in fact signed fewer than 100, mostly minor pieces of legislation into law, fewer than the nine most recent presidents.
This year he tried and failed to get legislation repealing President Obama's health care law through Congress, and saw his travel ban cracking down on immigration from a list of Islamic nations curtailed by the courts. There is no sign of construction beginning on the border wall with Mexico.
Clearly, there is more to do in 2018. And Trump says he will be working through Christmas as well.
"We'll be working in Florida, I'll be working very hard during Christmas because we have many things we're talking about, including North Korea, including a lot of things happening in the Middle East as you know," he said.
