Larry Downing/Reuters

Updated February 24, 2015

Remember President Obama's first veto? Probably not. Though it took him less than a year to reject any legislation, the move came on what was essentially a duplicate spending bill. How about his second veto? That was pretty obscure, too—the president objected to some of the details in the Interstate Recognition of Notarizations Act of 2010, which he was concerned would have unintended effects.

The third time will be, if not exactly a charm, more memorable. On Tuesday, Congress sent a bill to the White House that was intended to force approval of the Keystone XL pipeline. And Tuesday afternoon, Obama vetoed it, as the White House had promised he'd do.

"The Presidential power to veto legislation is one I take seriously. But I also take seriously my responsibility to the American people," he wrote. "And because this act of Congress conflicts with established executive branch procedures and cuts short thorough consideration of issues that could bear on our national interest—including our security, safety, and environment—it has earned my veto."

The quiet rejection is, as my colleague Russell Berman noted in November, the likely dividing line between two eras. Up until this week, Obama has issued the fewest vetoes since James Monroe. From the point the ink dries on the Keystone threat, he's likely to start using his Cross Townsend black roller-ball pen more frequently.

For example, Senate Majority Leader Mitch McConnell has pledged to attach budget riders to stop the EPA from enforcing new climate-change regulations. But he may be spared the opportunity to veto by Senate Democrats. Since his party still maintains a sizable minority in the chamber, it can filibuster to block a great deal of legislation. McConnell could threaten (or follow through on a threat) to tighten filibuster rules, leading Democrats to use the tool sparingly. There are also bills, like the Keystone bill, that attract the support of some Democrats, so that the party line breaks and bills can overcome the filibuster threshold.

The interesting thing to watch about Obama vetoes for the remainder of his term—"the fourth quarter," as he is fond of calling it—is that he'll be deploying them not so much to prevent affirmative changes to the law that he opposes, but to prevent Republicans in Congress from reversing laws that he signed during the opening stretch of his presidency.

In fact, one good way to understand the Obama presidency would be to consider it in terms of the way he used a pen in each of his three vetoes. During the first stretch, from 2009 to 2013—but especially from 2009 to 2010, when Democrats held a supermajority in the Senate and had control of the House—he used it to sign major legislation, from the Lilly Ledbetter Fair Pay Act to the Affordable Care Act. During the second, which seems to have drawn mostly to a close, Obama was in what he and his team referred to as the "pen and phone" era, in which he used the phone to try to persuade and the pen to issue executive orders. That period spanned from the beginning of 2014 until Obama's executive action on immigration in late November. With his veto this week, the president is likely ushering in a third and final act.

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