A former spokesman for Hillary Clinton Hillary Diane Rodham ClintonREAD: Cohen testimony alleges Trump knew Stone talked with WikiLeaks about DNC emails County GOP in Minnesota shares image comparing Sanders to Hitler Holder: 'Time to make the Electoral College a vestige of the past' MORE went after President Trump on Sunday following a tweet the president posted that appeared to mock the rising calls for him to release his tax returns.

"Congratulations, you just confirmed for every single person that marched yesterday that it was well worth their time," former spokesman Nick Merrill tweeted Sunday, after sharing the president's tweet.

Congratulations, you just confirmed for every single person that marched yesterday that it was well worth their time. https://t.co/KY02TYzMjr — Nick Merrill (@NickMerrill) April 16, 2017

Trump tweeted Sunday that someone should "look into who paid for the small organized rallies yesterday."

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"The election is over!" he tweeted.

His tweet came a day after thousands of protesters across the country gathered on what is traditionally Tax Day and urged him to release his tax returns.

More than a dozen people were arrested in Berkeley, Calif., over the weekend after violent clashes erupted in the streets between pro-Trump and anti-Trump groups.

Throughout his presidential campaign, many critics called for Trump to release his tax returns.

Trump had said he was under audit and would release the returns after the IRS finished his audit. He later dismissed the calls for him to release the documents, saying voters weren't interested.