Republican presidential candidate Donald Trump is holding nothing back after his 2016 rival Sen. Marco Rubio (R-FL) attacked his stance on immigration reform.

Rubio joined Democrats and liberals—as well as most of the mainstream media—in attacking Trump for calling out international criminals who exploit America’s weak and insecure border to get into the United States illegally.

“Trump’s comments are not just offensive and inaccurate, but also divisive,” Rubio said. “Our next president needs to be someone who brings Americans together – not someone who continues to divide. Our broken immigration system is something that needs to be solved, and comments like this move us further from – not closer to – a solution. We need leaders who offer serious solutions to secure our border and fix our broken immigration system.”

Rubio’s statement follows what Trump said about illegal aliens two weeks ago in his presidential campaign announcement speech. “When Mexico sends its people, they’re not sending their best,” Trump said then. “They’re sending people that have lots of problems… they’re bringing drugs, they’re bringing crime. They’re rapists. And some, I assume, are good people.”

Rubio joins people like Barack Obama’s 2012 presidential campaign co-chair and liberal actress Eva Longoria—who compared Trump to Adolf Hitler—and Univision programming president Alberto Ciurana–who compared Trump to Charleston, South Carolina, mass murderer Dylann Storm Roof. There are plenty of others throughout the mainstream media and institutional left who have slammed Trump as well, and some Republicans like former Texas Gov. Rick Perry and former New York Gov. George Pataki.

Sending out a link to a Breitbart California article detailing how one such illegal alien like the criminals Trump called out in his announcement speech allegedly murdered a woman in San Francisco on Wednesday, Trump launched his initial response at Rubio via Twitter: “Our Southern border is unsecure. I am the only one that can fix it, nobody else has the guts to even talk about it.”

“Our Southern border is totally out of control. This is an absolutely disgraceful. situation,” Trump added. “We need border security!”

“Where are the other candidates now that this tragic murder has taken place b/c of our unsafe border,” he added in another tweet. “We need a wall!”

In a fourth tweet, Trump sent a message directly to Rubio: “.@marcorubio what do you say to the family of Kathryn Steinle in CA who was viciously killed b/c we can’t secure our border? Stand up for US.”

In addition, a Trump adviser sent a lengthy statement to Breitbart News on Friday evening signaling that the real estate mogul isn’t backing down.

“Mr. Trump will never apologize for wanting the American people to have a secure border,” the Trump adviser said. “He is the sole candidate who will secure our broken southern border by building a massive wall. The American people deserve a wall to protect their safety, jobs and economy.”

In addition, Trump’s adviser told Breitbart News that his boss can’t wait to expose Rubio’s weakness on immigration:

Marco Rubio has zero credibility on securing our border. Nothing has been more “divisive” than the outright lies Marco Rubio used to try and sell his amnesty for illegal immigrants to the American people. Hard working Americans cannot depend on Senator Rubio to protect their jobs. Senator Rubio’s “Gang of Eight” bill, which was such an epic failure it never even came up for a vote in the House, would have given President Obama the immediate power to grant amnesty to millions of illegal immigrants.

Trump’s team seems ready to hone in on Rubio’s biggest weakness: That he worked with senior Democrats like Sens. Chuck Schumer (D-NY), Dick Durbin (D-IL), and the now-indicted Bob Menendez (D-NJ) to put forward an amnesty bill last Congress. Rubio eventually backed away from his own bill after he tanked in the polls.

“Rubio flip flopped on the bill for political expediency with the explanation that he could not expect President Obama to enforce it. Why would Rubio have given Obama this authority in the first place?” Trump’s adviser said.

Just this past weekend in New Hampshire, Rubio used several of the same talking points he used to sell the Gang of Eight bill to push a pathway to citizenship for illegal aliens. When asked if he supports a pathway to citizenship for those who broke America’s immigration laws, Rubio said: “I do.”

But first we have to prove to the American people that illegal immigration is under control and today that lack of confidence has made it impossible for us to make progress on immigration reform. So the first thing we have to do is we have to pass real reforms that secure the border more secure than it is today, an entry-exit tracking system to prevent visa overstays, and we also need to create an Electronic Verification system for employers so they can verify that the people they’re hiring are legally here. We need to put that in place and show it to the American people and prove that illegal immigration for the future is under control. After we do that the second step is we must modernize our legal immigration system. Today, legal immigration is primarily on the basis of whether or not you have a relative living here. In the 21st century it must be based on what skills you have or what you can contribute economically. After we’ve done those two steps, I believe the American people will be very generous and responsible about what you do with those who have been here a long time. I think the best approach is to have them come forward, undergo a background check, pay a fine for having violated our law, start paying taxes—and in return for all of that—they will get a work permit that will allow them to work and travel legally in the United States. That’s the only status they would be allowed to have for at least a decade. Then assuming if after a decade they’ve complied with all of that then they would be allowed to apply for permanent residency just like anybody else would—not through a special path—and then of course once you have permanent residency depending on how you acquire it, within three to five years, you could apply for citizenship. That is a long path. But I do think it’s fair and reasonable. But we can’t even get to that third step I’ve outlined until we’ve done the other two things first. That’s just the reality of the political situation we have today in America.

Rubio made most of the same claims in nearly identical language during his advocacy for the Gang of Eight bill.

Trump has also been extraordinarily critical of the Obamatrade deal that Rubio voted for.

“Rubio’s dangerous amnesty bill and his recent vote for Trade Promotion Authority – after never reading the Trans-Pacific Partnership – show an unsettling truth,” Trump’s adviser told Breitbart News.

Trump’s team compared Rubio at that point to Obama himself—both of them, after all, were first-term U.S. Senators when they launched their White House bids.

“Rubio is a typical politician who is controlled by the special interests,” Trump’s adviser said. “The one-term Senator simply does not have the experience or judgment to be President.”

Trump’s adviser wrapped his statement to Breitbart News by noting that Trump will actually secure the border, unlike Rubio.

“Mr. Trump believes that a nation without borders is not a nation at all,” Trump’s adviser said. “Mr. Trump will never apologize for fighting for border security. It is common sense and will Make America Great Again!”

Trump is likely to turn the jets on Rubio, as Rubio continues sinking in the polls again—much like he did after he drove amnesty through the Senate last Congress. In an exclusive interview with Breitbart News in Trump Tower in New York City after his presidential campaign announcement, Trump said of Rubio: “I would say Marco Rubio is just not the guy.”

“Rubio is weak on immigration and he’s weak on jobs,” Trump said in a previous interview with Breitbart News. “We need someone who is going to make the country great again, and Rubio is not going to make the country great again—and neither is [former Florida Gov. Jeb] Bush.”