Before she was a royal-in-waiting, Meghan Markle said on a television talk show that she might move to Canada rather than live in a country governed by a misogynist like Donald Trump. Prince Harry recently interviewed Barack Obama on the Today programme, giving the former president several opportunities to cast shade on his successor. The Sun quoted a senior UK government source saying that the royal couple want the Obamas at their wedding.

It is tempting for people on the left to see Markle and Harry as potential allies, in the belief that political divisions in recent years have been redrawn on cultural rather than economic lines. Around the world, fascists and their sympathisers have gained visibility and in many countries entered government. The stakes have risen, and politics has polarised. Maybe some of the royals aren't so bad, after all, whatever they once wore to a fancy dress party, and even if the leader of Windsor Council hoped to use the wedding as an excuse for Thames Valley Police to force homeless people off his town’s streets.

For the sake of minimising the violent and racist impact of the rise of the right, those on the left must decide who they will co-operate with, and how much they are willing to compromise. Some people also believe they have to ask whose interests could be sacrificed.

A woman of colour entering the highest levels of the British establishment and using her platform to lambast Trump would enlarge the voices of other women and people from minority ethnic backgrounds, and might advance their interests too. But it would also give legitimacy to the political self-expression of every other member of the royal family, and strengthen the undemocratic elements of the British constitution.

Meanwhile, some leftist Remainers and soft-Brexiters, including those who want to protect freedom of movement, are co-operating with liberal Thatcherites, such as George Osborne, who attacked migrants’ rights when they were in power but now say they want to defend an ‘open society’.

Such co-operation may make tactical sense, but the idea that a grand coalition between the left and pro-market liberals could be a solution to the rise of authoritarian nationalism ignores the roots of right-wing populism. Supporters of Trump and Brexit are not, as much commentary implies, uniformly working class. Far from it. But the current upheaval has been energised by an awareness that political and economic life are weighted strongly in the favour of some, and against the interests of others. The right has exploited this discontent. If the left is to provide a long-term solution, it cannot delay acting on either class inequality or racism.

Leftist social movements have allied themselves with centrist establishment elements before, with mixed results. The 'third way' project of New Labour and the Clintonite Democrats absorbed sections of the anti-racist, environmentalist, feminist and gay rights movements into the neoliberal project. That was possible because some of those campaigners had become less focused on reducing state violence and class inequality. Networked into the state, they were able to make substantive but limited advances.

This co-option of marginal ideas and people may enable painfully slow progress, but it is also easily exploited by reactionaries. Since 2007, crisis and austerity have encouraged resentment of political and economic elites, and much of the anger has been directed at those elites’ liberal factions and their uneasy – or in many cases unwilling – allies: oppressed groups and the social movements that represent them. Ukip and the EDL see no contradiction in attacking both neoliberal politicians and working-class migrants. For them, the qualified achievements of radicals who allied with centrist liberals – the amendment of the Race Relations Act, gay marriage – are direct attacks on their ‘way of life’ because they slightly undermine the structures of privilege.

The less powerful partner in a coalition rarely does well out of the relationship, however contingent or even imaginary it is. They are frequently blamed for failures and perceived as collaborators, and there is no reason to think this pattern will change. Elites are once more seeking to ally themselves to liberatory social movements and those they represent, and once again the price to be paid for this alliance is ignoring the way those elites exploit both their 'allies' and those who are left behind.