Sen. Rand Paul's (R-Kentucky) attack ad. YouTube Sen. Rand Paul (R-Kentucky) is taking his criticism of GOP presidential rival Donald Trump to the next level.

Paul's campaign released an online attack ad against Trump on Wednesday that blasts him for past statements praising Democrats and left-leaning policies.

"In many cases I probably identify more as a Democrat," Trump says in a clip from a 2004 interview featured in Paul's ad. "I've been around for a long time and it just seems that the economy does better under the Democrats than the Republicans."

In another part of the ad, Trump declares that now-Democratic presidential candidate Hillary Clinton is a "terrific woman."

"I'm a little biased because I've known her for years. I live in New York, she lives in New York, and I've known her and her husband for years. And I really like them both a lot," Trump says in the clip.

Paul's campaign said the ad is online-only and "will run through the weekend in Iowa and New Hampshire."

Asked about the ad during CNN interview later in the day, Trump defended his record.

He insisted he needed to praise — and give contributions to — Democrats like Clinton in order to win government favors. Trump suggested, however, that the political system is corrupt and businessmen like him shouldn't be able to influence politicians that way.

"If you look at Hillary Clinton, I contributed to everybody. I was a businessman — a world-class businessman. I built a net worth of much more than $10 billion," he said. "Everybody understands that. ... I don't think it's a great thing for the United States. I'm not sure that the system should work that way. But as a businessman, I did what other businessmen did and I contributed to everybody. Everybody liked me."

Trump dismissed Paul's other attacks as "old stuff" and then trashed his opponent.

"You look at a guy like Rand Paul: He's failing in the polls, he's weak on the military — he's pathetic on military," he said, offering a backhanded compliment to Paul's work as an ophthalmologist. "I actually think he's a far better doctor than he is a senator."

He also pointed to last week's indictment against pro-Paul political operatives working for a super PAC supporting his campaign. The indictment was related to their 2012 work on the campaign of Paul's father, Ron.

"Rand's campaign is failing. Hasn't his whole team been indicted?" Trump asked. "So he's a mess — there's no question about it."

View Paul's ad below: