W HEN OPPOSING political parties both think they are winning, one of them is usually wrong. This is the quandary America finds itself in, after the Democrats won the House of Representatives in the suburbs, while the Republicans tightened their grip on the Senate in the sticks. It also describes the attitudes of both parties towards the most divisive issue of the Trump era: immigration. Whipped up by a frenzied nativist intervention by President Donald Trump, including a closing TV ad so racist that even Fox News would not air it, most Republicans ran on the issue in the mid-terms. Democrats mostly tried to ignore it. Who was right?

The picture, again, looks mixed. The most virulent nativists lost, including a trio of Trump wannabes, Lou Barletta and Corey Stewart, Senate candidates in Pennsylvania and Virginia, and Kris Kobach, the Republican running for governor in Kansas. So did prominent Democrats who took the opposite tack—including Andrew Gillum and Beto O’Rourke, liberal darlings in Florida and Texas, both of whom wanted to rearrange the Immigration and Customs Enforcement ( ICE ) agency. But all had tough races. The broader conclusion from the mid-terms is that, on immigration and otherwise, both parties turned out their voters, extending their territory a bit, without taking from the other. It is tempting to see this as a validation of both their immigration strategies.

Exit polls, which suggested about half of voters liked Mr Trump’s immigration policies or wanted tougher ones, also support that. So do interviews with Democratic strategists. None thought Mr Trump’s late onslaught, which also included dispatching a small army to defend America against a weary column of Honduran asylum-seekers, had hurt their party. Several noted that his immigration policies, including his putative border wall, caging of migrant children and threat to deport 800,000 immigrants, known as DREAMERS , who were brought to America illegally as children, are all unpopular. Such complacency, on the issue that fuelled Mr Trump’s rise, on which Democrats remain most vulnerable to him and, for that matter, on which liberals are falling across the Western world, feels like a death-wish.

It ignores how asymmetrically the two parties are affected by partisanship, in which attitudes towards immigration, the most polarising issue, play a big part. The bumper representation given to small states in the Senate means Democrats need to win more conservative places than Republicans need to win progressive ones. And they cannot win there on scrapping ICE . The harder line taken by Democratic senators running in such states illustrated that. In Indiana Joe Donnelly declared himself a fan of the wall; in Missouri Claire McCaskill said she liked the sound of “Operation Faithful Patriot”, as Mr Trump’s fatuous troop deployment was called. Yet both lost, because in the end voters reckoned they were Democrats—the party, according to Mr Trump, of open borders.

It is not possible to say this was the reason for their defeat. But it is likely, because of another sort of immigration-related asymmetry. Only a handful of voters understand the details of immigration policy. Why otherwise do voters in West Virginia, where immigrants are rarer than millionaires, worry about them so much? Rather, as that example suggests, the issue is a repository for broader anxieties and allegiances. Even conservatives who think Mr Trump’s promised wall is nuts are keen on the sense of security, nationalism and contempt for liberal feelings it is meant to impart. Democratic opposition to Mr Trump’s draconian measures, which conservatives hear as the bleating of a party weak on security and captured by Hispanic activists, makes them even more appealing. In the hands of a skilled opportunist like Mr Trump, immigration is scarcely a policy problem at all. It is a means to rally nativist sentiment to win power.

Republicans maintain that, to the contrary, it is the Democrats who have commandeered the issue for political purposes. They are right to a degree. As the Democrats have become more dependent on Hispanic voters, they have become much keener to discuss migrant rights than border enforcement. Hillary Clinton barely mentioned it in 2016. And the fact that few Democratic mid-term candidates would say how many Hondurans should be allowed, or denied, entry revealed the same failing. Yet the conspiracy theory this has fuelled on the right—that Democrats are trying to boost illegal immigration to swell their electorate—is a fantasy.

Recent Democratic administrations have built as much border fortification as Republican ones. Barack Obama, the symbol of his party’s non-white coalition, deported more illegal immigrants than his predecessors. Last year Chuck Schumer, the Democratic leader in the Senate, offered to secure $25bn for Mr Trump’s border wall in return for protection for the DREAMERS . The Democrats’ main error on immigration is not to have been too political about it, but the opposite. They have primarily viewed immigration as a policy problem, to be unpicked through bipartisan compromise. Mr Trump’s response to Mr Schumer, which was to demand more draconian restrictions, including a cut in legal immigration and no more “shithole” Africans, should have disabused them of that. The president does not want a big bipartisan deal on immigration. He wants to keep it as a campaign issue.

Sandbagged by unreality

By ignoring immigration, the Democrats will let him have it—and when his name is on the ballot, in 2020, the onslaught will be fiercer. They need to redefine the issue, to draw some of its poison. That should start with a realisation that a party unwilling to speak of immigration as a security issue, as well as a humanitarian one, is unacceptable in much of America. A statement of zero tolerance for illegal immigration and a willingness to accelerate the processing of asylum claims could help relay that. Democrats need to take the politics of immigration more seriously. Mr Trump has sandbagged them with it once—and could easily do so again.