Political Capital with John Harwood

Romney's 'Zero Sum' Capital Gains Tax Plan

Mitt Romney

Fred Thompson's rivals don't intend to let him hold the spotlight if they can help it. You can see that in Mitt Romney's release of new tax-cut details this week.

Romney has said for months that he aimed to cut the capital gains tax for middle class investors to zero. But he didn't spell out how he'd define middle-class--until this week, as Fred Thompson was dominating the news with his belated entry into the race.

It's a broad (and therefore politically-appealing) definition--families earning less than $200,000 would pay nothing on capital gains income. His campaign says that would apply to 95 percent of American households.

The political effect of becoming more specific is twofold: Romney gets credit for offering a new tax-cut idea that might provide popular support, and he increases pressure on rivals to provide more detail on their plans for a core GOP priority. That's harder for Thompson, since his late start has left him short of time for policy development as well as building organization.

To be sure, all the Republican candidates will face pressure to sharpen their answers on the economy in time for the CNBC/MSNBC/Wall Street Journal debate on economic issues on Oct. 9th in Dearborn, Michigan. But Romney's new detail is another sign that time before voting starts is drawing short.

Tune in for our exclusive interview with Mitt Romney--on his tax plan and other issues--on CNBC's "Street Signs" this afternoon.

Questions?  Comments?  Write to politicalcapital@cnbc.com.