Sen. Marco Rubio on Sunday declined to condemn former President Donald Trump for his remarks Saturday about the husband of Republican rival Nikki Haley, a National Guard officer now deployed overseas.

"I think they're part of the increasing nastiness of this campaign and every campaign in American politics," he said on CNN's "State of the Union," adding in a comment that suggested that ugliness and mudslinging were beyond the control of the candidates themselves: "It's just part of these campaign cycles."

Trump brought up Haley's husband during a speech at Coastal Carolina University in South Carolina, suggesting something else was motivating his absence from her campaign other than service to his country. “Where’s her husband? Oh, he’s away. He’s away. What happened to her husband?” Trump said Saturday.

Maj. Michael Haley is serving an active-duty deployment in the Horn of Africa for the South Carolina Army National Guard. "If you mock the service of a combat veteran, you don’t deserve a driver’s license, let alone being President of the United States," Nikki Haley said later in response to Trump's comments.

But the Florida senator said that no matter what Trump said about anything, he would continue to back him. "I support him because Joe Biden's a disaster," he said.

Host Jake Tapper pointed out that Rubio himself had denounced Trump during the 2016 campaign when he mocked then-Sen. John McCain (R-Ariz.) for having been captured when his A-4E Skyhawk was shot down during the Vietnam War.

"I was running for president against Donald Trump and we were in a campaign," Rubio said.

Rubio also sparred with Tapper at length over the particulars of legislation recently negotiated by Sens. James Lankford (R-Okla.), Chris Murphy (D-Conn) and Kyrsten Sinema (I-Ariz.) that sought to alter American immigration policy, saying the reforms would have been worse than doing nothing at all.

"It wasn't a border security bill. It wasn't tough," Rubio said.

The measure died in the Senate last week only days after it seemed like it might attract bipartisan support.

"I’ve never seen an about-face like this in the 20-plus years I’ve been in politics,"