John McCain at the VFW post in Merrimack, New Hampshire, Dec. 29.
Photo: Andrew Cline

The presidential primary that will begin this evening is turning into a fairly clear-cut contest between the left and right wings of both parties. The question that will begin to be answered this evening is whether conservatives will control the Republicans — and whether liberals will lead the Democrats.

The Los Angeles Times reported Wednesday that the Republican Party "has become so splintered by the presidential primary campaign that some party leaders fear a protracted nomination fight that could hobble the eventual nominee." It's not just the Republicans who are divided, however. Both parties are undergoing internal struggles between moderate members and those who are more extreme.

The primaries have become ideological contests — left versus right — a division that became evident in national polls conducted in November and December and recently compiled by Gallup.

The ideological division between conservatives and moderates is clearer in the Republican primary. According to Gallup, 57 percent of moderate-to-liberal Republicans support former New York mayor Rudy Giuliani or Sen. John McCain. Only 22 percent of the moderate-to-liberal Republicans back former Arkansas governor Mike Huckabee, former Massachusetts governor Mitt Romney or former senator Fred Thompson. However, 56 percent of the conservative Republicans polled by Gallup favor one this threesome.

(Go here for the Gallup story on the Republicans; here for the Gallup story on the Democrats.)

The same pattern — though not as strong — appears on the Democratic side. Gallup found nationally that 57 percent of the conservative Democrats support Sen. Hillary Clinton; only 16 percent of this group (one in five Democratic voters describe themselves as conservative) support Sen. Barack Obama. Clinton has a much smaller lead among liberal Democrats — leading Obama 39 percent to 29 percent in this group. Former senator John Edwards collects 22 percent of the conservative Democratic voters and 28 percent self-described liberals.

What is likely to happen as the primary season moves along is for candidates to be weeded out — and that could exacerbate the conflicts within the two parties. With the Gallup numbers as a guide, when the Republican race narrows down to one of the conservatives (either Huckabee, Romney or Thompson) versus one of the moderates (McCain or Giuliani), the conservative would clearly have the advantage.

The divide on the Democratic side isn't as large — but once that race narrows down to Clinton versus either Obama or Edwards, then the New York senator may be in trouble because there simply are very few conservatives left in the Democratic Party.

Clinton has her strongest support nationally among seniors, women, lower- and middle-income as well as less-educated Democrats, Easterners and Southerners. Her lead among these demographic groups ranges from 22 to 35 percentage points over Obama and Edwards.

Among Republicans, according to Gallup, religion also differentiates the candidates. Huckabee receives support from 26 percent of the Republicans nationally who say they go to church weekly. He gets the backing of only 8 percent of those who seldom or never go to church. Giuliani, meanwhile, is supported by 17 percent of those who attend church weekly and 34 percent of those who seldom or never attend services.

Alan Abramowitz teaches political science at Emory University.