Keystone backers scramble for last vote on bill, Boehner warns Obama against veto This Nov. 14, 2014 photo shows a depot used to store pipes for Transcanada Corp's planned Keystone XL oil pipeline in Gascoyne, N.D. Democratic Sen. Mary Landrieu was racing to win over one last senator in the run-up to a critical vote on the Keystone pipeline set for Tuesday evening, with not only the energy project but her political future potentially at stake. So far, 59 senators have publicly voiced support for the bill which would green-light the pipeline -- one short of the 60 needed to secure passage and send the legislation, for the first time, to President Obama's desk. Obama, as well, is under pressure to sign the bill should it clear the Senate. House Speaker John Boehner warned Obama that if he vetoes, "It would be the equivalent of calling the American people stupid." He said: "A Keystone pipeline veto would send the signal that this president has no interest in listening to the American people." Landrieu is trying to win over Democratic converts to push the pipeline forward, but also help her struggling Senate runoff bid. Landrieu was forced earlier this month into a Dec. 6 runoff against GOP Rep. Bill Cassidy, and swiftly has resurrected the Keystone bill to demonstrate her Washington clout. The House passed its own bill last Friday, with help from Cassidy. But whether Landrieu can corral 60 votes in the Senate is an open question. All of the Senate's 45 Republicans are on board as "yes" votes. Support from Landrieu and her Democratic co-sponsors, and commitments from three more Democrats, bring the total to 59. The Louisiana Democrat has been adamant in her belief she will eventually get to 60, and supporters warn not to count her out. However, her possible road to passage narrowed Monday as Sens. Amy Klobuchar, D-Minn., and Carl Levin, D-Mich. -- two potential flips -- reaffirmed they would vote "no." Maine independent Sen. Angus King left the possibility open, though, telling reporters he was a "probable no." Landrieu will have another opportunity to lobby colleagues at Tuesday's caucus luncheon. Not surprisingly, several liberal Democrats are actively lobbying against her on this vote -- Sen. Brian Schatz of Hawaii, for example, blasted an email to supporters on Monday asking them to sign a petition against Keystone. Despite Republican warnings, if the bill passes, the White House has indicated the president would veto the measure. Landrieu said last week that neither the Senate nor House has the two-thirds majority needed to overcome a veto. But the vote offers a preview of what is ahead for Obama on energy and environmental issues when the Republicans take control of both houses of Congress next year. Even if the measure fails Tuesday or passes and is vetoed, Republicans in both chambers vowed to try to approve Keystone again. For six years, the fate of the Keystone XL oil pipeline has languished amid debates over global warming and the country's energy security. The latest delay came after a lawsuit was filed in Nebraska over its route. The proposed crude-oil pipeline, which would run 1,179 miles from the Canadian tar sands to Gulf coast refineries, has been the subject of a fierce struggle between environmentalists and energy advocates ever since Calgary-based TransCanada proposed it in 2008. Fox News' Kara Rowland and The Associated Press contributed to this report.