Last week, President Obama announced that he would veto the expected congressional approval of the Keystone XL pipeline. Negative reaction, even by some Senate Democrats, was swift. Sen. Joe ManchinJoe ManchinBiden: Negotiating assault weapons ban more difficult than infrastructure, reconciliation deal Biden says expanding Medicare to include hearing, dental and vision a 'reach' Biden says paid leave proposal reduced from 12 to 4 weeks MORE (D-W.Va.), a co-sponsor of the Senate bill, said that he was "extremely disappointed" in the president's announcement. Sen. John HoevenJohn Henry HoevenHouse passes legislation to strengthen federal cybersecurity workforce The 19 GOP senators who voted for the T infrastructure bill The Hill's 12:30 Report - Presented by Facebook - US gymnast wins all-around gold as Simone Biles cheers from the stands MORE (R-N.D.) stated that the president's "veto threat [was] no surprise." Top Senate Republicans, including new Majority Leader Mitch McConnellAddison (Mitch) Mitchell McConnellBiden says he's open to altering, eliminating filibuster to advance voting rights Pelosi says GOP senators 'voted to aid and abet' voter suppression for blocking revised elections bill Manchin insists he hasn't threatened to leave Democrats MORE (Ky.) and John CornynJohn CornynCornyn raises more than M for Senate GOP Is the Biden administration afraid of trade? The Hill's Morning Report - Presented by Facebook - After high drama, Senate lifts debt limit MORE (Texas) decried the announcement.

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Why would Obama veto the bill? The White House announced that the president is worried that bill passage would truncate "the thorough consideration of complex issues that could bear on U.S. national interests." Late last year, Obama expressed concern that the pipeline would not lower the price of gas and previously argued that the pipeline would not have the positive impact on jobs that supporters believe. Sen. John ThuneJohn Randolph ThuneSenate Republicans raise concerns about TSA cyber directives for rail, aviation Democrats narrow scope of IRS proposal amid GOP attacks Senate GOP signals they'll help bail out Biden's Fed chair MORE (R-S.D.) believes that Obama "is listening to his left-wing base." So, perhaps the president is acting on ideology alone.

Some pundits, however, have argued that a veto of the Keystone project would be key campaign fodder for 2016 presidential hopefuls. For example, Paul Bledsoe suggests that "Keystone will now be front and center in the presidential cycle." Is Obama looking forward to the immediate legacy of his administration?

There may be another possible reason why Obama issued a veto threat, especially so early in the 114th Congress. A few years ago, it was suggested that Obama used veto threats "to shame Republicans for their positions and fire up the liberal base." I suggest the he may be participating in "veto bargaining." Although the number of presidential vetoes has diminished in recent presidential terms (Franklin Roosevelt issued 635; Bill Clinton issued 37; George W. Bush issued 12; Obama, thus far, has issued two), the idea of veto bargaining suggests that a mere veto threat may induce Congress to alter its actions. In particular, political scientist Charles Cameron suggests that a veto threat may lead Congress to "anticipate vetoes and modify the content of legislation to head them off," which suggests that the president use the veto to "not only to block legislation but to shape it." Thus, the power of the veto cannot be measured merely in the number issued. It has been noted previously that "Obama has retreated from such threats in the past, citing changes which he said made the earlier measures more palatable if still distasteful to him." I would suggest that rather retreat from the threats, Obama used them to extract concessions from lawmakers.

It appears that Obama's veto threat may very well imperil the bill itself — or at least the likelihood that the Senate GOP can make it "veto proof." Hoeven has stated that the GOP "may not have enough to overcome a veto." Because McConnell has committed to allowing an amendment process, leaders in both parties have proposed amendments that make the bill more palpable to others — including Obama. However, Sen. Chuck SchumerChuck SchumerSchumer endorses democratic socialist India Walton in Buffalo mayor's race Guns Down America's leader says Biden 'has simply not done enough' on gun control The Hill's 12:30 Report - Presented by Altria - Manchin heatedly dismisses rumors of leaving Democratic Party MORE (D-N.Y.), who has a list of suggested amendments that might appeal to the president, has still urged Obama to veto the Keystone bill because he believes Democrats in the Senate could withstand a veto override vote.

Hoeven, though, hopes that the amendment process will be "the key to greenlighting Keystone." There should be concern, however, on the part of Senate Republicans that too much outreach to the Democrats could have the opposite impact. One key Democrat, Missouri's Claire McCaskillClaire Conner McCaskillEx-Rep. Akin dies at 74 Republicans may regret restricting reproductive rights Sunday shows preview: States deal with fallout of Ida; Texas abortion law takes effect MORE, who currently supports the Keystone oil pipeline, said last week that "[i]f Republicans try to 'basically take all power away from the EPA [the Environmental Protection Agency] or do some other really damaging things to the environment through the amendment process, it will be a very difficult decision in terms of final passage.'"

In short, by threatening the veto, Obama may have instigated passage of a bill with enough liberal amendments that he can abide the entirety. Alternatively, he may have begun a process intended to ensure widespread, bipartisan passage that may backfire on Senate Republicans.

Either way, President Obama's veto count might remain at two — but he would weathered his first storm of the 114th Congress.

Gibson is an associate professor of political science at Westminster College in Missouri.