Donald J. Trump says Bernie Sanders has planted protesters at rallies to stir things up and provoke violence.

Sanders denies it categorically.

Now a Florida congressman — a Trump supporter — says Hillary Rodham Clinton’s campaign is guilty of prodding the Trumpsters into striking back at the protesters.

No word yet from the Clinton campaign; I’m quite sure there’ll be a categorical denial there, too.

Conspiracy theories have this way of never dying. JFK assassination? Area 51 cover-up? 9/11?

It might be that long after this campaign has ended, we’ll hear conspiracy theories kicked around about who started the violence at the Trump rallies as the candidate stumps for the Republican Party presidential nomination.

Here’s my theory.

Trump started it by inflaming his crowds from the podium.

Punch people in the face? Beat the “crap” out of someone? Offer to pay legal fees for those charged with crimes?

The candidate is inciting the violence and that — all by itself — is what gives this story its staying power.

I get that violence has occurred over many decades. The 1968 Democratic National Convention provoked a full-scale series of street riots in Chicago. Police vs. Protesters turned into the stuff of hideous, actual “reality TV” for those of us who watched it unfold.

It spilled onto the convention floor. Security personnel beat up delegates and media reporters.

Do you recall hearing pols exhorting protesters from the stage? Neither do I.

Yes, this campaign is vastly different.

It has brought the level of political campaigning to a level not seen by anyone, near as I can tell.

It’s also prompted the goofballs among us to suggest that it’s all being orchestrated by mysterious evil political opponents.

It’s not so complicated. The violence is a result of a candidate fomenting the anger expressed by those who support his bid for the presidency, which has dared those who oppose him to respond with protests.

Why in the name of sanity — and decency — can’t Donald J. Trump start delivering a positive message of change?

I hope it isn’t too late.