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But if Collins is not the Republican nominee, Republicans will likely struggle to retain the seat. If former Secretary of State Charlie Summers — a likely Republican alternative — ran against either Michaud or Pingree, the incumbent members of Congress would have a decided advantage. Michaud leads Summers 57-32 percent, while Pingree holds a 50-39 percent edge.

Collins is the only Republican senator up for reelection in 2014 that comes from a state won by President Obama in 2012.