President Obama is poised to make the third veto of his presidency, putting the kibosh on a bill passed by both the House and Senate authorizing the Keystone XL pipeline.

Obama has so far exercised his veto less frequently than other recent presidents. President Bill Clinton vetoed 37 bills in eight years, and President George W. Bush vetoed 12 in his two terms. In President George H.W. Bush’s single term, he vetoed 44 bills.

But because Obama is facing some of the least productive Congresses in recent history, his low veto count may not be entirely of his own making. To compare him with other presidents, it makes more sense to look at the rate at which he has vetoed bills, rather than the overall tally.

To date, according to GovTrack, just shy of 3,000 bills have passed both houses of Congress during Obama’s terms, and he has rejected only 0.1 percent, compared with the average veto rate of 1.9 percent for all other presidents since 1973 (not including Obama).

His sparing use of the veto cannot be explained simply as the result of working with a Democratic-controlled House and Senate for the first two years of his presidency. When Obama’s veto rate is parsed more finely, he has still used the veto less frequently than other presidents facing comparable Congresses.

When facing “friendly” Congresses (president’s party controls both Senate and House):

Obama’s veto rate: 0.1 percent

All other presidents (1973-2008): 0.7 percent

When facing split-control Congresses:

Obama’s veto rate: 0 percent

All other presidents (1973-2008): 3 percent

When facing opposition-controlled Congresses:

Obama’s current veto rate: 0 percent

veto rate: 0 percent Obama’s veto rate if he vetoes Keystone : 1.4 percent

: 1.4 percent All other presidents (1973-2008): 3 percent

In his final two years in office, Obama’s use of the veto is expected to rise as he confronts a Republican House and Senate. Although George W. Bush had a relatively low veto rate when facing an opposition-controlled Congress (0.5 percent), most recent presidents have resorted to the veto more frequently, with Clinton, George H.W. Bush and Reagan vetoing 2.6 percent, 3.6 percent and 4.7 percent of the bills that crossed their desks, respectively.

PERCENTAGE OF BILLS VETOED PRESIDENT ALL ALLIED SPLIT CONGRESS ALL OPPOSED Obama 0.1% 0.0% 0.0% Bush, G.W. 0.1 0.0 0.5 Clinton 0.0 — 2.6 Bush, G.H.W. — — 3.6 Reagan — 2.7 4.7 Carter 1.5 — — Ford — — 2.5 Nixon/Ford — —⁠ 3.9

However, Donald Ritchie, the historian of the U.S. Senate, cautioned that Obama may not catch up with the average veto rate for presidents facing Congresses controlled by the opposing party. Even when they’re in the minority, Senate Democrats can still play defense for the president, Ritchie pointed out. “You have the president’s party in the Senate blocking cloture votes, so they never get the bill to veto,” Ritchie said.

As the Senate has shifted to requiring supermajorities as a matter of course, it has become a more powerful shield for presidents who wish to avoid using a veto. The Democrats still retain 44 seats in the Senate, which is enough to deny the Republicans a supermajority and to protect Obama from high-profile confrontations not of his choosing.