Democrats are right to think that Donald Trump’s prejudicial comments about Hispanics are a stick with which they can spend the next four months beating Republicans. But though the perception that the GOP has embraced hate is perhaps their greatest asset in 2016, they are making a mistake if they think they are completely invulnerable when it comes to immigration. That’s why their party line opposition to bills creating a mandatory minimum sentence for illegals convicted of felonies and stripping federal funding from sanctuary cities was an unforced error that could help cost them any chance of winning a competitive race in Pennsylvania, which could decide control of the Senate. Both bills were successfully filibustered by Democrats yesterday in a move that could come back to haunt them in November.

The bill, known as “Kate’s Law,” is just about the only aspect of the debate about immigration that works in the GOP’s favor. It’s named after 32-year-old Kate Steinle, who was murdered by an illegal immigrant that had already been deported four times for criminal behavior. The alleged killer, Juan Francisco Lopez, had nonetheless been released by the San Francisco after an arrest without informing Immigration and Customs Enforcement (ICE) because of the city’s sanctuary cities law that forbade officials from assisting federal authorities in enforcing immigration laws.

Sanctuary cities are a popular talking point for Republicans since they run afoul of the basic concept of the rule of law. You don’t have to agree with Donald Trump about building a wall and buy into the fantasy that all 11 million illegal immigrants are going to be deported to understand municipalities have no right to defy the federal government, let alone to obstruct ICE or to grant impunity to those who have entered the country illegally. Indeed, if the U.S. Supreme Court has already made clear that President Obama had no power to unilaterally change immigration laws by granting amnesty to millions via executive order, San Francisco certainly doesn’t have a leg to stand on to try to do the same thing. Nor does Philadelphia, for that matter.

This issue could play a not insignificant role in the re-election campaign of Pennsylvania Senator Pat Toomey, the sponsor of a companion bill to “Kate’s Law” that focused on funding for sanctuary cities. Newly elected Philadelphia Mayor Jim Kenney had reversed a decision by his predecessor and reinstituted one of the most aggressive and extreme examples of sanctuary city regulations. That puts Toomey’s Democratic opponent Kate McGinty on the defensive. She dares not oppose a measure supported by her party’s liberal base, especially in its Philadelphia stronghold, while also understanding just how much damage this does her in the rest of the state. Her attempt to straddle the issue by calling for some changes in Philadelphia’s non-cooperation with federal authorities while making it clear she doesn’t oppose the sanctuary cities concept has satisfied no one.

Toomey’s bill would have placed municipalities in desperate need for federal funds in a tight spot. In particular, Philadelphia would have lost $39 million in community development block grants. But the dependence of Kenney and the Democratic machine that elected him last year on minority voters has caused them to dig in, which puts McGinty between a rock and a hard place.

So long as they are merely pointing out Trump’s foolishness and hate speech, Democrats are on firm ground on immigration. But their unwillingness to take a stand against sanctuary cities puts them on the wrong side of concerns about law enforcement and terrorism, a point that Toomey didn’t hesitate to make in the last week. It isn’t racist to note that Kate Steinle wouldn’t have died had San Francisco behaved in a responsible fashion and not treated her killer as someone whose illegal status gave him a “get out of jail free” card. Treating support of such irrational ideological stands on immigration as a partisan litmus test for Democrats may not be enough to elect Trump, but it will damage the party especially in down-ballot races. That isn’t just “red meat” for Trump supporters. It’s a sign that Democrats have confused understandable sympathy for law-abiding immigrants for willingness to discard the rule of law. That’s too heavy a burden for candidates like McGinty, who stands to be hurt badly by the controversy outside of Philadelphia. It’s also a signal that, whatever Trump’s fate, the GOP may be able to hold onto the Senate this year after all.