Democrats are favored to hold Tom Allen's House seat, but they shouldn't ignore the possibility of a GOP pickup.

Allen's decision to run for the U.S. Senate could make the first district seat vulnerable, says Nathan Gonzales, the political editor for non-partisan The Rothenberg Report, which analyzes congressional races. The report has the Allen seat listed as "Democrat Favored."

Gonzales couldn’t say if the rating applied to all six Democrats seeking the nod to replace Allen:Stephen Meister, Michael Brennan, Mark Lawrence, Ethan Strimling, Chellie Pingree and Adam Cote. Dean Scontras and Charlie Summers are seeking the GOP nomination.

The district traditionally leans Democrat, but not by a huge margin, Gonzales said. In the 2004 election, Democratic presidential candidate John Kerry won 55% in the first. Allen has held the seat since ousting one-term GOP Rep. James Longley in 1996 by a ten point margin.

The rating could change as the races progress, Gonzales said.