Rep. Joaquin Castro (D-Texas), the manager of the Democratic presidential campaign of twin brother Julián Castro, dismissed calls from the Trump campaign and other Republicans Tuesday to delete a tweet identifying some of President Trump’s biggest Texas donors.

Why it matters: Castro posted the names and occupations of 44 Trump donors from San Antonio ahead of the president's planned visit Wednesday to El Paso following Saturday's mass shooting there.

Context: A racist post attributed to the suspected gunman speaks of "invasion." That word was used in Trump campaign Facebook ads approximately 2,200 times, according to CNN data analysis — a point Castro picked up on as he defended his Monday night tweet.

The writer of the anti-immigrant screed said his opinions pre-date Trump's presidency.

The big picture: Anyone who donates over $200 to campaigns must report to the Federal Election Commission.

The Washington Examiner notes that while such donors' names can be found via the FEC, some Republicans criticized Castro because his tweet seems to target specific local citizens of his own congressional district.

What he's saying: President Trump Wednesday by tweeting, "I don’t know who Joaquin Castro is other than the lesser brother of a failed presidential candidate (1%) who makes a fool of himself every time he opens his mouth."

"Joaquin is not the man that his brother is, but his brother, according to most, is not much. Keep fighting Joaquin!"

Editor's note: This article has been updated with Trump's comments.