Neither fundraising nor the building of grass-roots organizations in key primary states is driving the Republican presidential race. Endorsements haven't mattered much either. Stump speeches have been of minimal importance. And policy papers—such as former Massachusetts Gov. Mitt Romney's 59-point economic plan or ex-Utah Gov. Jon Huntsman's proposal for tax rate cuts—have been largely overlooked.

By far the biggest influence on the Republican contest has been the series of nationally televised debates. There have been more debates than ever—six so far—and they have attracted record audiences. The most recent debate on Sept. 22 on Fox News drew more than six million TV viewers, plus another six million watching on streaming video.

The debates have overwhelmed the Republican race. "They are about all there's been to the campaign," says Fox political commentator Brit Hume. After each debate the campaign has been frozen until the next one, except for arguments over issues spawned by the debates themselves.

Gov. Rick Perry's policy of offering instate tuition at Texas colleges for illegal immigrants, and his effort to require 12-year-old girls to be inoculated against HPV virus, became prominent issues once he was pelted with questions about them in the debates. When Mr. Romney attacked Mr. Perry's position on Social Security, it emerged as a front-burner issue. Mr. Perry gave the issue a news hook by calling Social Security a "Ponzi scheme."

While Mr. Romney's record in Massachusetts was always going to be a major issue, the debates have made it more so. The same is the case with Mr. Perry's opposition to erecting a fence across the U.S. border with Mexico.

Another effect of the debates has been to make the Republican race more combative than it might otherwise have been, at least this far ahead of election year. The media like conflict, encourage it, and have succeeded in generating it.

The impact of the debates on the candidates has been palpable. After three poor debate performances last month, Mr. Perry dropped out of first place in polls. He fell to 17% in the ABC News/Washington Post survey in late September, from 29%. He trailed Mr. Romney (25%) in that poll and was tied with businessman Herman Cain.

The reverse is true for Mr. Cain. His conservative message and personal appeal in debates have increased his support to 17% in the ABC News/Washington Post poll in late September, from 3% in late August.

Rep. Michele Bachmann of Minnesota has risen, then plummeted, chiefly because of debates. With a strong performance in the June 11 debate on CNN, she was included for the first time in the Rasmussen presidential preference poll, getting 19%. Less impressive in more recent debates, she's slipped in the Rasmussen poll to 8%.

The rise and fall in poll numbers reflects the normal fickleness of voters in the early stages of a multicandidate presidential campaign. But the debates have reinforced the tendency to rotate from one candidate to another.

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