Americans baffled by Congress’s inaction on measures to limit access to guns typically point to a familiar scapegoat: contributions from groups such as the National Rifle Association to (mostly Republican) members of the House and the Senate.

There’s an immediacy to this association that is comforting. People see that polls show broad support for, say, expanding background checks for gun purchases and wonder why nothing gets done. So we look at the money those politicians have taken. Thousands of dollars to those corrupt politicians in Washington! Of course they’re not going to vote for new gun laws when the NRA is spending thousands and thousands of dollars getting them elected. The idea adheres to our existing sense of what corruption looks like, and clearly any politician who rejects the will of the electorate must be somehow corrupt.

If this is any part of the rationale behind opposing new gun controls, it’s only a tiny part.

Shortly after the massacre in San Bernardino, Calif., we looked at NRA contributions to members of Congress who had been criticized for offering only “thoughts and prayers” in response. Thousands of dollars seems like a lot in the abstract, but as a percentage of the total amount that politicians receive, it’s pennies.

If you include independent expenditures made on behalf of candidates, the percentage from pro-gun groups is larger. It is also true that gun rights groups (such as the NRA) spend far more in political contributions than do gun-control groups. According to the Center for Responsive Politics, gun rights groups spent about $3.6 million supporting members of Congress in 2016, compared with $260,000 spent by gun-control groups. Again, though, that’s a small percentage of total spending, which topped $4 billion in congressional races that year.

So if it’s not money that motivates (mostly) Republicans in Congress to block gun-control measures, what is it?

First, gun politics are more complicated than they are often presented. Yes, most Americans — nearly all, really — support expanded background checks. But asked whether they support stricter gun laws, opinions are much more split. An October CNN-SRSS poll found that a slight majority of Americans supported stricter gun laws.

A poll from Quinnipiac University in June found that 57 percent of Americans thought it was too easy to buy a gun, still a majority but not the huge majority that supports expanded background checks.

CNN’s poll didn’t find any substantial difference by age when considering the question of stricter gun laws.

Where there was a difference was by party. Nearly two-thirds of Republicans oppose stricter gun laws, including almost half who oppose them strongly. Among Democrats, opinions are stronger in the other direction — but among independents, the question is about split.

If you’re a Republican lawmaker, then, why would you advocate strongly for stricter gun laws? Your base of support opposes the idea, and swing voters are split.

And if you’re President Trump, the result is even starker. Three-quarters of your base opposes stricter gun-control laws, more than half strongly. Where’s the incentive to advocate for them?

In 2015, NBC and the Wall Street Journal asked Americans how they felt about a number of groups. The two most popular groups in the country were Planned Parenthood … and the NRA.

That those are the two groups that evoked the strongest reactions explains why they did: partisan sentiment. Democrats strongly support Planned Parenthood and Republicans the NRA. The NRA’s investment in promoting its message to Republicans broadly has certainly contributed to the Republican base’s views on the subject, but it’s not clear how strong those views would have been without the NRA’s powerful presence in the political conversation.

After all, this is also a moment in which partisan sentiment is a significant and inescapable driver of political attitudes. The Pew Research Center has measured partisanship for years and finds an increasing skepticism and hostility from members of one party toward the other. In 2016, more than 4 in 10 members of each party thought the other side was a threat to the United States.

If you are a Republican who sees Democrats calling for new gun-control measures, that might easily be conflated with your negative views of Democrats regardless of what the NRA’s position is on the subject.

Pew’s research found something else that is significant in this conversation. Republican voters most strongly agree with their party’s position on guns than on any other subject. More than Republican policy on the economy, on the deficit or on abortion.

Democrats, though, are less fervent. Gun policy is, overall, one of the issues on which Democrats generally have the least agreement with their party.

Again, there’s a valid question about the extent to which the NRA has helped foster that partisan, cultural sense of how guns should be handled legally. But there’s little question at all that if the NRA stopped giving money to politicians tomorrow, we’d soon see new legislation restricting guns in the country.

Members of Congress do hear from people about gun issues. A Pew study released in October found that gun owners were more likely than non-gun-owners to contact public officials to discuss gun policy — and a plurality of them did so to argue that gun laws are too strict.

Republicans control the House, the Senate and the White House, and the Republican base opposes new gun controls. For advocates of new policies limiting gun ownership, that’s a much bigger problem than the NRA giving a few thousand dollars to a dozen members of Congress.