Politico provided some context:

President Donald Trump on Monday criticized former Vice President Joe Biden for his involvement in passing the 1994 Violent Crime Control and Law Enforcement Act.

Biden, who chaired the Senate Judiciary Committee at the time, did play a central role in getting the 1994 bill passed, and it has loomed over his presidential bid, with critics saying the bill generated mass incarceration that disproportionately affected minorities.

However, Biden has defended the bill and his role in passing it, and denied that it resulted in mass incarceration, though former President Bill Clinton apologized in 2015 for signing the bill into law, saying he “made the problem worse.”

Now, this is legitimate criticism and one that has already been made by some of Biden’s fellow Democratic candidates.

However, it is not a criticism that Donald Trump can bring up. 

And the Twitterverse was quick to point out why.

Like I said bringing up Biden’s support for that 1994 crime bill is a reasonable thing to do during a campaign.

However, if you are a racist POS, who has energized the White supremacist movement in this country, and inspired numerous hate crimes, it is probably best if you kept your big fat fucking mouth closed. 

P.S. I would also like to point out that insinuating that the man who served as the VP to the first black President of the United States is any kind of racist is laugh out loud funny.