This is a rush transcript from "Your World," April 22, 2015. This copy may not be in its final form and may be updated.
NEIL CAVUTO, HOST: You know, Senator John McCain was the first Republican, of course, to run against President Obama. And now he is a lapdog for President Obama? Look at this.
(BEGIN VIDEO CLIP)
SEN. RAND PAUL, R-KY.: But I'm the only one actually standing up and saying the war in Libya was a mistake. The bombing of Assad would make ISIS stronger. The arms to the Islamic rebels would make ISIS stronger.
So I'm really the one standing up to President Obama. And these people are essentially the lapdogs for President Obama. And I think they're sensitive about that.
(END VIDEO CLIP)
CAVUTO: So, I immediately said, guys, we have got to call Senator John McCain.
CAVUTO: He is here.
Senator, lapdog, what do you think?
SEN. JOHN MCCAIN, R-ARIZ.: Well, one of my colleagues said today -- he said, yes, McCain and Graham are a couple of -- are lapdogs. They're a couple of Doberman pinschers.
MCCAIN: It's -- I put it this way. Senator Paul is the worst possible candidate of the 20 or so that are running on the most important issue, which is national security.
And talking about being wrong, in 2007, he said Iran would be -- it would be ridiculous to call Iran a threat to the United States' national security. Last summer, he publicly doubted whether ISIS was a threat to the United States' national security.
The list goes on and on. In 2011, he proposed a budget that would have cut defense by 30 percent. In 2011, budget would have eliminated all foreign assistance to Israel. He said Iran isn't a threat to Israel.
His -- the record is very clear that he simply doesn't have an understanding about the needs and the threats of United States' national security.
CAVUTO: What he did say, to be fair to the senator, though, Senator McCain, is that, in this case, if you look at the early push on the part of folks like you and Lindsey Graham to immediately intercede in Syria and to deal and take on Assad head on would have resulted in something far worse, and we're seeing it played out now, and that you missed that, and that that was something serious.
MCCAIN: Neil, Neil...
CAVUTO: What do you say to that?
MCCAIN: Neil, please.
We said you have got to arm the Free Syrian Army. The entire national security team, David Petraeus, head of CIA, Hillary Clinton, secretary of state, Leon Panetta, secretary of defense, all recommended...
CAVUTO: No, I understand, Senator. But he's saying -- isn't he saying that those people -- if you had done that, you would be arming what came to be ISIS?
MCCAIN: If we had armed them, Bashar al-Assad would have been overthrown, and we would have had a nation; 200,000 people wouldn't have been slaughtered with millions of refugees, one of the greatest genocides committed in recent history by Bashar Assad.
He was about to go. It was the president of the United States himself who said it's not a matter of when -- of whether, but when Bashar al-Assad is going to leave. Dempsey, the chairman of the Joint Chiefs of Staff, Panetta -- and Panetta both said it's inevitable that Bashar Assad will go.
So we watched while the Iranians came in with 5,000 Hezbollah, tons and tons of equipment, training...
CAVUTO: All right.
MCCAIN: ... the Iranian Revolutionary Guard. Neil...
CAVUTO: Well, no, no doubt, Senator.
CAVUTO: And, as you said to me, it's all water under a very bloody bridge, and you're quite right.
But now you mentioned at the outset particularly sharp criticisms of Senator Paul that he is the worst of that bunch running for president right now on these issues.
CAVUTO: So if he were your Republican nominee up against Hillary Clinton, who would you vote for?
MCCAIN: Yes. I would support the nominee of my party. I am a loyal Republican.
I would hope that good sense would prevail here, because the realities of the world today doesn't allow for the isolationist policies. We have already seen what happens from -- quote -- "leading from behind," leading from far behind. And that's what Rand Paul would do.
But I would hope that many of us could prevail on him to see the world in a very different light. But I'm not going to not support the nominee of my party.
CAVUTO: Is he the worst of the presidential candidates then within the party right now?