The idea of open borders underpins many of the American left’s current stances on immigration. Although this isn’t always stated explicitly, it explains both the vehement opposition to Trump’s proposed wall on the border with Mexico (whose construction actually began under Bill Clinton) and the insistence on rolling back regulation on immigration flows.

Yet this is a weak position, for at least two reasons. First, states presuppose borders. Failing to control borders is not an immigration policy, but the lack of one. It’s also a position likely to reinforce the already widespread perception that immigration flows are “out of control”.

Second, the case for open borders relies on premises that are more usually associated with the libertarian right than the liberal or social-democratic left. The idea is that allowing the “invisible hand” of the market to determine where people live will benefit everyone because workers will naturally move to where there is more demand for them. But the left has historically been skeptical of that premise – holding instead that markets need to be regulated in order to lead to socially optimal outcomes.

A stronger case in favor of immigration – that’s also more coherent with the left’s traditional values – can be built on demographic data. This is not something the American left has paid much attention to so far. Yet, the evidence is clear: net of immigration, the US population is both shrinking and ageing at an alarming rate.

If the trend continues, it threatens both the economic vitality of the country as a whole and widely cherished welfare programs such as Social Security and Medicare, which require a young and economically active tax base.

The right’s response is to call for Americans to have more children. But this only makes sense on the chauvinistic assumption that immigration is a threat for the country’s civic culture. Immigration is a faster and more efficient way to replenish the country’s work-force.

The left should therefore seize on the demographic data and openly make the case that the United States needs more immigrants, not just because cultural diversity is a good in itself, but also because this is essential to maintain current levels of economic growth and welfare provision.

One way to tailor immigration flows specifically to the country’s demographic needs is through a points-based system like those of Canada and Australia. Yet this is not absolutely necessary; all the available evidence shows that even low-skilled immigrants more than pay for themselves in terms of tax revenue, beginning with the second generation. (First-generation immigrants cost the fiscal system marginally more than they contribute, largely because they have more children.)

A more plausible objection concerns immigration’s distributive effects. Both the nationalist right and, more recently, some currents of the hard left have argued that immigration negatively affects certain sectors of the population, because it increases competition among workers and puts downward pressure on wages and working conditions.

In reality, the empirical evidence for these claims is far from conclusive. But even if these claims were undeniably true, it wouldn’t necessarily be a weakness of the left case for more immigration, since it shifts the debate to a terrain on which the left should be happy to argue.

If the problem is that immigration harms certain sectors of the population while increasing aggregate levels of growth, then surely the response should be to call for more economic redistribution alongside higher levels of immigration, so that everyone benefits from the added wealth generated by immigrants.

The same goes for working conditions. If there’s any reason to suppose that immigration adversely affects workers’ rights, it’s because a large proportion of the immigrant workforce is currently illegal, which makes it harder for them to unionize and claim the rights legal workers are entitled to.

Presumably, any policy aimed at fostering the number of immigrants entering the country would have to grant them the same rights as legal workers. So, it could actually end up bolstering the bargaining power of organized labor.

There doesn’t have to be a tradeoff between immigration and welfare programs or workers’ rights. On the contrary, they are two sides of the same coin.

The United States needs more immigrants to maintain current levels of economic growth and welfare provision, but it also needs more economic redistribution and workers’ rights to make sure that the aggregate benefits of immigration are shared fairly within society as a whole.