Is President Trump losing sway over Republicans? It would seem so in Alabama, where the candidate he endorsed, Sen. Luther Strange, is trailing in the state’s GOP Senate primary. In an average taken of all polls for the Sept. 26 runoff, former state Supreme Court Chief Justice Roy Moore leads Strange 45 percent to 36 percent. Strange’s deficit comes after also finishing second to Moore in the initial primary.

If Strange does go on to lose the runoff (and there’s still nearly a month to go) — or even if it’s simply a close race — it would be easy to conclude that Trump has lost his ability to influence Republican primary voters. But maybe he never had much of that power to begin with.

The real lesson heading into the 2018 midterm cycle is that Trump should be smarter about who he endorses: “On-brand” endorsements can help, but Trump doesn’t have the power, for example, to make moderate Republicans vote for an uber-conservative, or vice versa.

Endorsements, if they work at all (and often they don’t), work best when they give an ideological cue to a voter that they wouldn’t have otherwise had. That’s why endorsements rarely matter in general elections: Most voters already fit into one of the partisan camps and are going to cast a ballot based solely off party label. In a primary, on the other hand, the candidates are more ideologically similar, and so an endorsement can help voters make a choice.

In 2010, for example, Sarah Palin endorsed fellow tea partyer Christine O’Donnell over the more moderate and well-known Mike Castle in the Delaware Republican Senate primary. Palin’s endorsement of O’Donnell specifically highlighted O’Donnell’s conservative positions, and though it may not have won O’Donnell the primary, according to polling data, it certainly helped her along.

Unlike Palin’s endorsement of O’Donnell, Trump’s endorsement of Strange never made a lot of sense from either a messaging or policy standpoint. Trump ran as an outsider. Strange is an incumbent U.S. senator backed by Senate Majority Leader Mitch McConnell and the pro-McConnell Senate Leadership Fund. He’s the “establishment” candidate.

Strange’s opponent Moore, on the other hand, is a lot more like Trump. Both Moore and Trump are populist politicians who have made a political career by running against the establishment. Moore ran against an incumbent Republican governor in a 2006 primary, for example. That’s not to say Moore and Trump are exactly the same. Moore has a religious appeal that has never been part of Trump’s shtick. Still, Moore fits the Trump model better than Strange does. It’s probably why Steve Bannon, Trump’s recently departed chief strategist, is now working to elect Moore.

And Bannon isn’t alone. Despite Trump’s endorsement, his constituency appears to favor Moore. The latest Opinion Savvy survey found that Moore leads Strange by 25 percentage points among likely runoff voters who strongly approve of Trump’s job performance. Strange has an 11-point advantage over Moore among the much smaller group of likely runoff voters who strongly disapprove of Trump. And although Trump dominated among non-college educated voters last year, a recent Cygnal/L2 survey showed that Moore was up by 52 percent to 28 percent among primary voters with only a high school degree or some college education. Strange led by a single point among voters with at least a college degree.

The Alabama Republican primary is not the first time GOP primary voters have gone against a Trump-endorsed candidate. Back in 2016, then-candidate Trump endorsed Renee Ellmers in a North Carolina congressional primary; despite holding very different policy views than her on immigration, perhaps the defining issue of Trump’s presidential bid. In the end, North Carolina voters voted for one of Ellmers’s opponents instead.

Now compare the Strange and Ellmers examples to what’s going on in the 2018 Arizona Republican Senate primary. Trump recently tweeted praise for Kelli Ward over incumbent Republican Sen. Jeff Flake. The reason for the accolades is fairly clear: Flake refused to vote for Trump in the 2016 presidential election and has written a book bashing Trump. Ward, meanwhile, has been pro-Trump and very anti-illegal immigration. Ward and Trump have similar ideologies and images, and Trump voters appear to recognize that fact. In this case, Trump helped give attention to a candidate his voters were already predisposed to like. So while Flake was in trouble before Trump ever said a kind thing about Ward, she has taken a double-digit lead over Flake since Trump’s tweets.

The lesson of these different endorsements should be fairly clear: Trump voters aren’t mindless drones. They’ll take cues from the president when he’s selling them on something it makes sense for them to back. Indeed, much of the reason Trump won in 2016 was because he defended positions that were already popular among the base, even if they weren’t popular among the party elite. On one of the biggest issues of the 2016 primary, illegal immigration, Trump staked out a hardline position that was already highly correlated with vote choice in previous primaries. (More anti-immigration Republicans did better, on average, in GOP primaries.) He took that position when one of the so-called frontrunners for the GOP nomination, Jeb Bush, was known for being soft on illegal immigration. Trump found a lot less success when he was pushing a health care bill this past spring and summer that went against his promises to Republican voters in the primary.

This has implications for the 2018 midterms — who comes out of the various GOP primaries — but it also says something about the landscape of modern American politics. In short: Trumpism isn’t limited to, or even (mostly) about, Trump.