Paul is always upbeat, but lately he's had more reason to be, as he sees libertarian ideas bubbling up from the grass roots.
"People outside of Washington are waking up," he told me, "and they're getting the attention of a few in Washington."
Paul has been in Congress more than 20 years, and much of that time he's played a lonely role, often being the only representative to cast "no" vote on bills to expand government.
"Twenty years ago, there weren't very many people around that would endorse these views. So ... I'm very pleased with what's happening. There are more now, but the problems are so much greater."
Because bigger government creates built-in resistance to cuts.
"Everybody has their bailiwick they want to protect: 'We know the spending is bad. But don't touch my stuff.'"
The biggest growth is in entitlements. Recently, after constituents yelled at them, Republicans backed off on their reasonable plan to try to make Medicare sustainable.
"This is one of the places where good conservatives and good libertarians have come up short. ... We get a bad rap that we lack compassion. A liberal who wants to take your money and give it to somebody else ... grab(s) the moral high ground."
At the recent Conservative Political Action Conference, Paul floated a novel idea: "Would you consider opting out of the whole system under one condition? You pay 10 percent of your income, but you take care of yourself -- don't ask the government for anything."
The CPAC crowed applauded. But liberals like MSNBC's Chris Matthews mocked him, sneering that anyone who accepted Paul's offer would have no access to federal highways, air safety, food inspection, cancer research or defense.
Paul laughs at Matthews' shallow criticism. Ever the constitutionalist, he'd like to privatize the federal highways someday, but he notes that even now they are largely financed by the gasoline tax -- essentially a user fee. As for air and food safety, he's sure the airlines and food companies have no desire to kill their customers and that careless companies would be disciplined by competition and the tort system. He claims that government stands in the way of a lot of cancer research.
In other words, it's foolish to assume that just because the government doesn't do something, that it wouldn't be done at all.
"(Matthews is) using fear," Paul said. "They all do that ... use fear to intimidate."
A member of my studio audience asked Paul about the coming vote to raise the debt ceiling.