Texas Democratic Rep. Filemon Vela was blunt and explicit in an open letter to presumptive GOP nominee Donald Trump on Monday.

"Mr. Trump, you're a racist and you can take your border wall and shove it up your ass," Vela wrote.

FILE - In this June 27, 2014 file photo, Rep. Filemon Vela, D-Texas talks to the media after touring the McAllen Border Patrol station, in McAllen, Texas. Vela said in an open letter Monday, June 6, 2016, that Republican presidential candidate Donald Trump's "ignorant anti-immigrant opinions," border wall rhetoric and continued attacks on a sitting federal judge "are just plain despicable." Gabe Hernandez, AP

Vela, who represents a district located right on the Mexican border, was extremely critical of Trump's rhetoric towards Latinos - especially his latest broadside against the Hispanic federal judge presiding over a case involving Trump University.

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His fiery letter was filled with seemingly pent-up frustration at Trump's rise.

"Your position with respect to the millions of undocumented Mexican workers who now live in this country is hateful, dehumanizing, and frankly shameful," the letter read. "The vast number of these individuals work in hotels, restaurants, construction sites, and agricultural fields across the United States. If I had to guess, your own business enterprises either directly or indirectly employ more of these workers than most other businesses in our country."

And in what has become a mostly bipartisan effort, Vela chastised Trump for his comments on Judge Gonzalo Curiel, who is presiding over one of the Trump University fraud cases. Trump has said Curiel's Mexican heritage should bar him from overseeing the case since Trump wants to build a wall to keep undocumented immigrants out.

"You have now descended to a new low in your racist attack of an American jurist, U.S. District Court Judge Gonzalo Curiel, by calling him a 'Mexican; simply because he ruled against you in a case in which you are being accused of fraud, among other accusations," Vela wrote. "Judge Curiel is one of 124 Americans of Hispanic descent who have served this country with honor and distinction as federal district judges. In fact, the first Hispanic American ever named to the federal bench in the United States, Judge Reynaldo G. Garza, was also from Brownsville, Texas, and was appointed by President John F. Kennedy in 1961."

For his part, Trump is not showing any signs of rescinding his criticism of Curiel. In an interview with Fox and Friends on Monday, Trump vigorously defended himself from claims that his attacks were a mistake.

"All I'm trying to do is figure out why I'm being treated so unfairly by a judge," Trump said. "And a lot of people agree with it. All I want to do - all I want to do is find out why am I being treated so unfairly by a judge?"

But there is a growing chorus of criticism. In the last week, Senate Majority Leader Mitch McConnell, Tennessee Sen. Bob Corker, Arizona Sen. Jeff Flake, Speaker Paul Ryan and even one of Trump's biggest boosters, former Speaker Newt Gingrich, all lambasted Trump for his comments.

On Monday, Florida Sen. Marco Rubio joined the back of the line.

"I think it's wrong," Rubio told WFTV in Orlando. "He needs to stop saying it... [Curiel] is an American."

"I don't think it reflects well on the Republican Party. I don't think it reflects well on us as a nation"

Recently, Rubio had taken his own share of blowback for saying that he would accept a convention speech slot to speak on behalf of Trump. The endorsement took many of his backers by surprise.

One former Trump presidential rival that is not criticizing him: Texas Sen. Ted Cruz. Cruz offered a "no comment" to CBS News when asked about Trump's attacks on Curiel.

Cruz set himself up as a staunch ally of Trump during the majority of his presidential run, even calling him "terrific" in December. Cruz changed his tone once Trump turned on him, questioning his eligibility for the presidency, attack the appearance of Cruz's wife, and pushing a National Enquirer story alleging that Cruz had affairs with multiple women.

Nebraska Sen. Ben Sasse, one of Trump's most forthright critics in the GOP, went a step further on Monday and called Trump's remarks "the literal definition of 'racism.'"

Public Service Announcement:

Saying someone can't do a specific job because of his or her race is the literal definition of "racism." — Ben Sasse (@BenSasse) June 6, 2016

The Trump campaign did not respond to a request for a response to Vela's letter.