Obama just issued his third-ever veto. Don’t expect many more.

Today, President Barack Obama vetoed a bill to fast-track construction of the Keystone XL pipeline. This was the third veto of Obama's presidency, and the first since 2010. With the GOP now in control of both houses of Congress, it might seem like the beginning of a new era, during which Obama will whip out his veto pen again and again.

But the makeup of Congress, the state of political polarization, and recent historical trends suggest otherwise. We're likely to see a few more vetoes from Obama, but not a ton.  Instead, the Senate's likely to remain the place where bold new bills go to die.

That's because the big question isn't about Obama's own preferences — it's whether the newly GOP-controlled Congress will be able to successfully pass many meaningful bills that he strongly disagrees with. And that answer depends on whether the  filibuster continues to be used so routinely — and on how willing Democratic senators will be to defect from the party line.

The filibuster will continue to block most bills from even getting to Obama

This term, Republicans have 54 seats in the Senate — meaning they'd have to peel off 6 Democrats to beat a filibuster. That's a tall order. Many of the conservative Senate Democrats most likely to defy party leaders have retired or been defeated in the past few years. A mere few, like Joe Manchin (D-WV), and Joe Donnelly (D-IN), remain — they're not up for reelection in 2016. The most endangered Democrats facing reelection this cycle are Harry Reid (D-NV), the party's leader, and Michael Bennet (D-CO), who's worked closely with party leadership and is unlikely to defect on important issues.

There are still enough Senate Democrats left to filibuster most contentious bills

And on the high-profile, contentious matters that might merit a presidential veto, Democrats have tended to be highly disciplined — like minority Senate Republicans were. The current battle over funding for the Homeland Security Department is a good illustration. Republicans are trying to pair this funding with a rollback of Obama's executive actions on immigration, but Senate Democrats have successfully filibustered this proposal four times. Republicans haven't managed to even peel off even one Senate Democrat in any of these votes.

The sort of bills Obama is likely to veto are those on topics like Keystone XL — where he (or at least his negotiating position) is somewhat to the left of his party, and many Democrats are therefore willing to defect. Policy toward Iran could be an issue like this — though an Obama veto threat has already led many Democrats to temporarily pull their support from a bipartisan Iran sanctions bill. Michael Shear and Coral Davenport of the New York Times also suggest that a bill to eliminate Obamacare's medical device tax could win bipartisan support — but paying for it could be a problem.

So if Mitch McConnell and John Boehner can come up with many more bills like Keystone, expect the vetoes to fly. But if not, it looks like Obama's final two years will feature just a few more vetoes — not a flurry. This would be consistent with the experiences of recent presidents facing an opposition Congress.

Presidents veto more when the opposition controls the Congress

There are more vetoes when the opposition runs Congress — but not as many more as you might think.

By our tallies — which exclude pocket vetoes and private bills —post-World War II presidents average about 5 vetoes in each two-year term when Congress is controlled by their own party or the two chambers are split. And they average 13 vetoes per term when both chambers are controlled by the opposition.

Averages spanning several very different political situations can be messy, but the experience of recent presidents has tracked this number quite closely. George W. Bush issued 11 vetoes from 2007-2008, his sole term where Democrats controlled Congress. Bill Clinton faced three terms where the GOP controlled Congress, and averaged 12 vetoes across them. And George HW Bush vetoed 15 Democratic bills from 1989-1990, and 14 in the following two years.

That's a little more than one veto every two months. And if the filibuster continues to be used effectively and the parties remain so polarized, Obama might be sent even fewer bills that he thinks deserve his veto.

Raw veto counts tell us more about Congress than the president

Shear and Davenport mention that Obama won't near Franklin Roosevelt's total of 635 vetoes. That is, of course, true — but that's more because of changes in Congress than the presidency.

If you look at the raw count above, the use of vetoes seems to have steeply declined since mid-century. Yet the vast majority of the bills vetoed by Roosevelt, Truman, and Eisenhower look like this:

These are known as "private bills," designed by Congress not to change public policy, but to give something to certain individuals or groups (often, to grant them money, benefits, or visas).

Private bills and pocket vetoes usually aren't very significant

This is a type of bill that was common in the late 19th and early 20th centuries — and was frequently vetoed by presidents who wanted to position themselves as opponents of patronage (notably Grover Cleveland). But Congress lost its enthusiasm for private bills around mid-century, and the number of private bills passed has plunged since. (None passed in 2013 or 2014.)

The veto chart above also includes what are known as "pocket vetoes." The Constitution says that a bill not returned by Congress to the president in 10 days will become law, "unless the Congress by their Adjournment prevent its Return, in which Case it shall not be a Law." There have been legal disputes over when, precisely, the pocket veto can be used, but in recent practice, it generally applied to bills passed by Congress near the end of a term. If Congress then leaves town, the president can let the bills die by taking no action.

These last-minute minor bills passed by Congress, like private bills, used to be far more common (and indeed, many were private bills). But according to a paper by political scientist Charles Cameron of Princeton, pocket vetoes "only rarely are of any policy significance," since substantive measures are usually passed earlier in the session. Cameron suggests that excluding them from the total leads to a more accurate tally of meaningful vetoes.

So we've done that in this chart, which shows far more modest variation among presidents:

As you can see here, going back to FDR, no president has averaged more than 8 regular vetoes of public bills per year in office — except for one, President Gerald Ford. Due to the post-Watergate Democratic landslide in 1974, Ford faced huge opposition supermajorities during the final two years of his short tenure. Accordingly, he repeatedly used the veto to send back their bills. Obama, on the other hand, still has enough Democratic senators to take care of that for him.

This piece was updated to reflect Obama's veto of the Keystone bill.

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