US President Donald Trump insults and attacks Democratic presidential contenders.
He doles out derisive nicknames.
Rarely, however, does he defensively respond to an attack, real or perceived, against him. He's done it twice in less than a week in response to former Vice-President Joe Biden, so it's worth examining how and why Biden manages to annoy Trump.
Biden's focus in his announcement video on Trump's infamous remarks after Charlottesville did what few politicians do effectively: call out Trump's narrative as a lie and challenge him as a racist.
Trump insisted that he had answered the question "perfectly," and then said (falsely) that the "very fine people" he was referring to "were protesting the taking down of the monument to Robert E. Lee."
"Everybody knows that," he lied.
The march was nothing of the sort: The chants were anti-Semitic, and the advance billing was directed at neo-Nazi groups.
Biden forced the President to relitigate one of the worst moments of his Administration, knowing Trump could not resist weighing in and doubling down on his cover story. Note to Democrats: Going back to poke Trump in the eye, now and then, reminds voters why they've come to dread hearing from him.
Today, Biden's candidacy aggravated Trump again, with the International Association of Fire Fighters' endorsement of the former Vice-President, which set off a Trump Twitter rant:
"I'll never get the support of Dues Crazy union leadership, those people who rip-off their membership with ridiculously high dues, medical and other expenses while being paid a fortune. But the members love Trump," one tweet said.
"The Dues Sucking firefighters leadership will always support Democrats, even though the membership wants me," read another a few minutes later. "Some things never change!"
To boot, the endorsement was particularly effusive.
"As the 2020 Democratic primary for president of the United States heats up, the IAFF is supporting the one candidate who will protect our members on the job, help keep fire departments fully staffed and support your right to have a voice in the workplace," the statement read.
"Based on his unequalled record on our union's basket of issues and our long-standing core value of having our friends' backs, the IAFF Executive Board - your elected representatives who make decisions on your behalf - has voted unanimously to endorse Joe Biden in his run for president of the United States in the Democratic primary."
And while Trump would like to differentiate between union leaders and members, the firefighters anticipated Trump's excuse mongering: "We did our due diligence and commissioned Zogby Strategies, a renowned national polling company, to conduct a poll targeting a sample of our 160,000 members who are likely to vote in their state's Democratic presidential primary. With a margin of error of 2.6 per cent, the results showed that Biden has a strong lead over all contenders in the Democratic primary."
Trump knows Biden's ability to draw on blue-collar voters undermines his ability to hang on to the Upper Midwest.
Union voters - first responders no less! - are supposed to be the voters Trump won over from the Democratic camp.
To the extent they bounce back into the Democratic column, Trump will have to start looking elsewhere - as his campaign manager Brad Parscale did over the weekend, by suggesting Republicans can improbably flip deep-blue New Mexico.
The Democratic website Shareblue crowed, "Trump is clearly scared about losing working-class white voters in 2020 - a group he desperately needs if he wants to win re-election. But attacking them for not endorsing him isn't likely to help win them over."
Well, that is true, but Trump is not thinking strategically.
He's lashing out at the guy who's invading his turf and who's showing Trump to be weak.
Another note to Democrats: When challenged for a group or region that Trump knows was key to his election victory, he's likely to say and do things that frankly aren't in his self-interest.
The candidates who can provoke him the most often will elevate their own profiles.