WASHINGTON (AP) — Democrats are grappling with an election-year dilemma posed by the Keystone XL oil pipeline.

Wealthy party donors are funding candidates who oppose the project — a high-profile symbol of the debate over climate change. But some of the party's most vulnerable incumbents are pipeline boosters Whether Democrats retain control of the Senate after the 2014 midterm elections may hinge on them.

The dilemma was highlighted Thursday as President Barack Obama's former national security adviser said Obama should approve the pipeline to send Russian President Vladimir Putin a message that "international bullies" can't use energy security as a weapon.

The comments by retired Gen. James Jones came as a top Democratic donor again urged rejection of the pipeline. Billionaire Tom Steyer vows to spend $100 million to help Democrats this year.