President Trump's effort to paint Joe Biden as corrupt — debunked by fact-checkers — fits a pattern of Trump's attacks on enemies: Raise deeply serious questions, regardless of what the facts say; hammer on those questions; never, ever seek finality.

Why it matters: Trump tries to plant seeds of suspicion and doubt, even if he doesn't actually prove a case. He incubates the attacks in perpetuity, rather than seeking an actual resolution. But in Biden's case, they've backfired in a way Trump couldn't have imagined.

How Trump does it:

Ask questions, raising the specter of wrongdoing.

Be vague and broad with accusations — specifics can be proven wrong.

Never seek finality. Once it's over, the innuendo is gone and the attack becomes stale.

The suspicions of wrongdoing are always more titillating than the real story.

This is how Trump has worked for years — and not just when there's an election opponent to beat:

1. When Trump promoted the "birther" conspiracy against Barack Obama.

It wasn't until Obama produced his long-form birth certificate in 2011 that Trump was forced to give it up, saying: "I was able to do something that nobody else could do."

2. When Trump leveled charges of voter fraud in the 2016 election.

He claimed millions of people voted illegally with zero evidence to support it.

In the face of continued questions, he formed a commission to look into the matter. After states declined to provide information, the commission disbanded.

3. When Trump accused Obama of tapping his phones.

After being continually pressed for specifics on the unfounded claim, the message from the White House evolved into broader activities of FBI surveillance on Trump campaign associates.

He later said the claim was based "on a little bit of a hunch."

4. When Trump cast "deep state" government workers as agents covertly working to undermine the policy aims of his administration.

The "deep state" has at turns been painted without evidence as a force loyal to Obama, Hillary Clinton or the "corrupt FBI" under James Comey.

But many of the officials who raised or supported accusations against Trump — including the inspector general in the Ukraine whistleblower story who deemed the complaint credible — were Trump appointees.

5. When Trump painted immigrants as criminals throughout his campaign and presidency.

Citing anecdotes and cherry-picking statistics without context, Trump has made his case against immigration by framing it as a threat to domestic safety.

By remaining vague, he has skirted statistics that show immigrants have lower crime rates in the United States.

6. When Trump hammered (and continues to hammer) Clinton over her emails and suggested corruption with the Clinton Foundation and the Uranium One deal.