President Trump on Sunday criticized the weekend protests against his presidency and those demanding the release of his tax returns, suggesting deep-pocked opponents “paid” for them and saying the 2016 presidential “election is over.”

At least 20 people were arrested Saturday at a park in Berkley, Calif., when attendees of a pro-Trump and an anti-Trump rally clashed.

Police in riot gear confiscated sticks, knives and fireworks that were being hurled in the melee, after failed efforts to separate the events with makeshift fencing.

“Someone should look into who paid for the small organized rallies yesterday. The election is over!” Trump tweeted Sunday.

The anti-Trump rally was one of about 150 across the country on Saturday to criticize the president’s policies and demand that he release his full IRS returns.

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Other events took place without major incidents in such U.S. cities as Chicago, New York, Seattle and Washington, D.C., and outside of Trump’s south Florida resort home, Mar-a-Lago.

Many of the events, on Tax Day, the deadline for hundreds of millions of Americans to file their IRS returns, were organized by the group TaxMarch.org, whose executive committee includes a former Occupy Wall Street protester.

Others helping organize the events Saturday included labor unions and activist groups such as MoveOn.org and Common Cause.

“I did what was an almost an impossible thing to do for a Republican-easily won the Electoral College! Now Tax Returns are brought up again?” Trump also tweeted Sunday.

That Trump will cave to the pressure and release his full tax returns appears unlikely, considering the president has said he won’t amid an ongoing IRS audit and the White House saying in January that he will not.

The Associated Press contributed to this report.