President Donald Trump complained on Sunday about the continued demand for his tax returns.

This comes the day after protests on April 15–the usual weekday deadline for people to file their tax returns. Demonstrators nationwide called on the president to release his. They rallied in cities like New York City, Washington D.C., and Chicago, as well as outside the president’s Mar-a-Lago resort in Florida.

Trump is not legally required to release his tax returns. And he didn’t, even during the height of the contentious 2016 campaign. However, this decision broke decades of tradition among viable presidential candidates, and became a constant source of ammo for his critics. Concerns generally center around how his international business earnings, and conflicts-of-interest might influence his ability to lead the county. He has constantly, and voraciously denied wrongdoing. Sunday’s tweet is simply another time he claimed the tax returns are no big deal.

Nonetheless, reporters have done their fair of digging. Last year, The New York Times got their hands on a portion of his 1995 returns, which suggested he could avoid paying income taxes for years. More recently, unidentified leaker(s) sent investigative reporter David Cay Johnston two pages of Trump’s 2005 returns, but his March appearance on The Rachel Maddow Show garnered a lot of mockery from journalists on social media. The new information was pretty standard, nothing incriminating.

But critics are still pushing, as indicated by Saturday’s marches. Here’s video of the Mar-a-Lago rally, as obtained by Palm Beach Post reporter:

The president also demanded Sunday that there should be some look into who funded the rallies.

One organization linked to the Saturday event is called “Tax March.” Via its website, it organized demonstrations, and solicited donations. They report that over 25,000 people participated in over 200 rallies nationwide. The executive committee includes people from the National Women’s Law Center, the National Working Families Party, and the Indivisible Project, a non-profit. The group is also partnered with organizations like the progressive MoveOn.org, reformist Americans for Tax Fairness, and 32BJ SEIU, a union of property service workers (eg. doormen, cleaners, window cleaners).

We’ve reached out to learn more about “Tax March.”

One member of the executive committee responded to the president’s first tweet.

As for Trump’s claim about Republican candidates winning the Electoral College being “impossible”: GOPers have often had strong showings in presidential contests since Abraham Lincoln won the 1860 race. More recently, President George W. Bush took the victory in 2004, winning 286 electoral votes to John Kerry‘s 251. He famously won the 2000 race despite losing the popular vote, just as Trump did in 2016. Bush’s dad arguably lost the 1992 campaign because of third-partier Ross Perot (though that’s debated). Ronald Reagan dominated the 1980 and 1984 races. In the former, he took 489 votes to Jimmy Carter‘s 49. In the latter competition, Democratic opponent Walter Mondale only took home state Minnesota.

[Screengrab via ABC]