Billionaire climate activist and Keystone XL foe Tom Steyer's political action committee is asking people to vote on the next Senate candidate to target with a TV attack advertisement -- and one of them is Sen. Mary Landrieu, D-La.

Steyer's NextGen Climate PAC typically bashes Republicans for promoting fossil-fuel-friendly policies -- and, to be sure, four of the five choices presented on the group's website are GOP candidates.

But by including Landrieu, one of the Senate's biggest Keystone XL boosters, Steyer's group could jeopardize Democrats' hold on the seat.

"Actually, Senator Landrieu, tar sands are one of the world’s dirtiest fossil fuels. Keystone XL would generate as much carbon pollution as 51 new coal-fired power plants," NextGen Climate said on its website, which also offers options to target Sen. Marco Rubio, R-Fla., and GOP Senate candidates Rep. Paul Broun of Georgia, former South Dakota Gov. Mike Rounds and West Virginia Rep. Shelley Moore Capito.

Landrieu's campaign did not immediately return a request for comment.

Landrieu is facing a tough re-election contest against GOP Rep. Bill Cassidy. She's also poised to become the chairwoman of the Senate Energy and Natural Resources Committee as early as Thursday, which would give her a perch to advance pro-oil and gas energy policies climate advocates like Steyer and environmental groups oppose.

Topping the list of such policies is Keystone XL. Opponents of the Canada-to-Texas pipeline say it would exacerbate climate change, as they note the oil sands it would transport are 17 percent more carbon intensive than traditional crude.

But its backers, citing a final State Department environmental report released Friday, say the pipeline won't ramp up greenhouse gas emissions because demand will bring oil sands to market regardless of whether it gets built.

Those supporters, which include business groups, unions, centrist Democrats and Republicans, say it also would bring jobs and strengthen U.S. energy security.

The State Department says the project would create 35 permanent jobs, though it would contribute 42,100 indirect and direct positions during the construction phase.

President Obama, however, has questioned Keystone XL's jobs impact.

When Bill O'Reilly brought up the 42,100 jobs figure in an interview with Obama that aired Monday, the president interjected that, "Well, first of all, it's not 42,000. That's not correct. It's a couple of thousand to build the pipeline." That was an apparent reference to the State Department's estimate that Keystone XL would add 3,900 construction jobs.

Obama has said he would reject Keystone XL if it "significantly exacerbates the problem of carbon pollution," a comment White House officials have reiterated this week following the release of the environmental report.