FORTUNE — House Majority Leader Eric Cantor is promoting the Romney-Ryan ticket as a team offering a credible, detailed plan for turning the country around. But some of those details proved troublesome in a sit-down interview with Fortune on Thursday.

The Virginia Republican said his party is laying out a path to salvage the long-term solvency of Medicare. And he took on President Obama for engaging in “scare tactics” over those entitlement reforms in the Ryan-authored House GOP budget. “At the same time, he is the one who is taking massive amounts of cash out of very popular programs like Medicare Advantage and the prescription drug program,” Cantor said. “This directly impacts seniors.”

It’s a point that Ryan himself made in his speech accepting the vice presidential nod on Wednesday night. Attacking Obama’s health care reform law, Ryan said its “biggest, coldest power play of all” targeted seniors for $716 billion in cuts. But Ryan’s own budget counted on those same savings, which in fact would be squeezed from reimbursement payments to hospitals and insurers. Asked about the inconsistency of Ryan attacking cuts his own plan embraced, Cantor begged off. “The assumption was that, um, the, the, ah, again — I probably can’t speak to that in an exact way so I better just not,” he said.

On tax reform, Cantor noted Romney is proposing a 20% across-the-board reduction in marginal rates — “that’s a fairly straightforward and specific idea that he’s talking about,” he said — as well as lower corporate rates. What Romney hasn’t specified is how he’d get there. For example, his plan doesn’t name any deductions in the current code that he’d cap or eliminate. President Obama hasn’t offered a full accounting, either, though he has named several, including taxing the earnings of investment fund managers as ordinary income instead of capital gains. That’s something Romney, the former Bain Capital executive, knows a lot about. He’s nevertheless remained mum on the issue so far.

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Cantor himself is forcefully on record in support of preserving the current treatment. “All I know is my position on carried interest is if you have actual risk at play, if you actually have capital at work, then there is an ownership interest in the underlying asset. It should be treated as such,” he said. “Now it’s a debate that we’re having with the other side. The difference is with the President.”

Reminded that Romney hasn’t spelled out his own view, Cantor said, “You’d have to ask him. I don’t know what his position is on that.” He said he expects a discussion of those kinds of specifics to unfold “over the next couple months.”

Cantor rose to power in the House with Ryan two years ago — co-pilots along with California Rep. Kevin McCarthy of a youthful Republican resurgence. Here in Tampa, he’s cut a notably low profile, though he remains a party-building force and is focused on helping deliver his home state to Romney. The economic recovery in Virginia is outpacing the nation’s, with unemployment at 5.9%. “But Virginia is very competitive and I think we’re going to win this election on the issue of jobs and the economy,” Cantor said.