Biden had a turbulent 24 hours earlier this month after his campaign confirmed he still supported the Hyde Amendment, which outlaws federal funding for abortions, following his commitment in May to abolish it. That sparked heavy backlash among his 2020 competitors and other progressives, leading him to reverse his position and declare that he could no longer support the amendment.
On Friday afternoon, Trump mocked the Democratic frontrunner and commemorated "National Flip-Flop Day" on Facebook.
"Since he now supports taxpayer-funded abortions AND open borders, I hope Joe Biden enjoys National Flip-Flop Day!" Trump wrote.
June 14 is a very busy day for the president as it is also Flag Day, the U.S. Army's birthday and his own birthday.
Both Trump and Biden had a war of words earlier this week, offering a taste of what a potential matchup would look like in a general election in 2020.