President Obama pauses at a wreath during a memorial observance ceremony at the Pentagon on Sept. 11, 2016, to commemorate the 15th anniversary of the 9/11 terrorist attacks. (Manuel Balce Ceneta/AP)

On Friday, President Obama vetoed a bill allowing 9/11 families to sue Saudi Arabia for not doing enough to stop the terrorists who killed their loved ones. It wasn't for his political benefit. That's according to Molly Reynolds, a congressional analyst with the Brookings Institution. Congressional leaders say they have enough support to override an expected veto, which would be a first in Obama's presidency.

Ahead of the veto, The Fix interviewed Reynolds by email to better understand what Obama was dealing with. Earlier this week, we talked to Middle East expert Jon Alterman with the Center for Strategic and International Studies about the bill's potentially negative geopolitical implications. The conversation below has been lightly edited for length and clarity.

THE FIX: What’s the political upside for the president, if any, to vetoing this bill?

REYNOLDS: There are very few political upsides to vetoing it. All of the arguments that the administration has made for why they oppose the bill are on policy and national security grounds, including the possibility that other countries would take similar steps and allow lawsuits against the United States, and the possibility of negative effects of the law on counterterrorism operations, especially in cooperation with other countries.

Congressional leaders say they have enough support to override the president's veto (a two-thirds majority in both chambers). Is Obama the only one in Washington opposed to letting 9/11 families sue Saudi Arabia?

Most of the lobbying we’ve seen against the bill has come not from domestic political constituencies but from foreign interests, including the Saudi government (which has spent a reported $5 million on the effort) and, this week, the European Union. (That’s not to say the measure has no domestic opponents; a large bipartisan group of former national security officials have also come out against it.)

So what's the case Obama's probably making to persuade lawmakers to uphold his veto?

Obama has made it clear that his veto is on policy and national security grounds and not merely because the Saudis, with whom the administration has had a complicated relationship, are pushing for the veto. That’s a relatively nuanced case to try to make.

Supporters of the bill, meanwhile, have a much more straightforward political argument: 9/11 families “deserve their day in court,” and “if the Saudi government did nothing wrong, they have nothing to be afraid of.” Not only does that case for the bill have the support of a politically powerful domestic political constituency (9/11 families), but it’s also much easier to explain to voters than the relatively more complicated policy grounds on which the Obama administration opposes the bill.

The election is 46 days away. How much is that playing into this debate?

Some members, particularly those in competitive races, may be wary of going on the record “against 9/11 families,” especially since the argument against the bill is much more difficult to explain. There are likely some legislators who could be persuaded to go along with the administration and vote against the override if it came after the election, in the lame-duck session, but who are wont to go on the record with that vote just weeks before voters cast their ballots.

For Republican supporters of the bill, meanwhile, the politics point toward an override for an additional reason: embarrassing the president on a foreign policy matter just before the election (political scientists refer to this kind of use of vetoes as blame game politics).

Is there any indication you’ve seen that Obama is gaining ground with Democrats to back his veto?

There have been a number of legislators — some from both parties, and especially in the Senate — who have expressed skepticism about the bill, mainly on the policy grounds articulated by the Obama administration.

The biggest challenge here is time. The administration had probably hoped that by waiting until the last minute to veto the bill, it would be sending the bill back to the Hill after the Senate had already recessed for the election, which it, for a time, looked like would happen sometime this week. But ongoing fights over a short-term spending bill to keep the government open past Sept. 30 have slowed down, and both chambers will be in session next week.

How historic would a veto override be?

Successful veto overrides are relatively rare. According to data from the Senate, the president has vetoed a total of 2,573 bills since 1789, and only 110 of these (about 4 percent) have been successfully overridden.

The last successful veto override was in 2008, when the House and Senate overrode President Bush’s veto of a Medicare bill.

In the contemporary Congress, overriding a veto requires cooperation between the two parties, since congressional majorities are not usually large enough for one party to supply all the votes.