This week was a vivid demonstration of the inability of conservatives to deliver results after the great populist revolts in 2016 in Britain and the United States. And it showed that there is a golden opportunity for liberals in both countries to tackle the public concerns that motivated the mistaken decisions to vote for Brexit and Donald Trump.

To put it bluntly, the Tories under Prime Minister Theresa May and the Republicans under President Trump have failed as governing parties. That’s because they can’t reconcile their inflammatory rhetoric with the practical realities of economic and social policy in the 21st century. The conservatives talked big to aggrieved voters, but they have come up empty.

This past week offered a rare chance to test the propositions on trade, immigration and other issues that have been polarizing British and American politics. Conservatives presented easy solutions — for Britain, a Brexit escape from a meddlesome European Union; and for America, a border wall (and other symbols) to address the real strains caused by immigration.

Republicans are trivializing Michael Cohen's crimes. Their cynicism is hurting the country. (Joy Yi, Kate Woodsome, Danielle Kunitz/The Washington Post)

But the conservative quick fixes didn’t work. They were ill-planned, half-baked, jingoistic responses to serious issues. Rather than remedy the inequities that bothered middle-class Brits and Americans, they instead sought to turn back the clock with proposals that simply didn’t fit today’s globalized world.

May’s Brexit plan was an attempt to negotiate an exit from the E.U. that she never fully believed in herself. She had to compromise to the point of incoherence because a hard Brexit and total separation would have been unworkable for Northern Ireland and unacceptable for Scotland, risking the potential breakup of the United Kingdom, not just its departure from the E.U.

Trump’s border mania was different. It has been political demagoguery dressed up as policy. The inflammatory campaign seemed to work the first time in 2016, helping Trump get elected, but not the second, in the midterms.

When Trump tried real policy to deal with immigration and trade over the past 18 months, he produced little. His fire and fury toward Mexico led to only modest revisions in the North American Free Trade Agreement, and his separation of migrant families as a deterrent to seeking asylum shocked the conscience of the country and the courts and has mostly been shelved.

And finally, Trump’s tantrum this week, threatening to shut down the government if he didn’t get his promised wall, embarrassed even Republicans. It was a sign of how empty Trump’s cupboard has become that political leverage is the threat to implode his own administration. Whatever else the past two years have shown, it’s that the Republicans under Trump could not govern effectively, even when they controlled both houses of Congress.

Well, those days are over. They lost their chance. What about the Democrats?

Now that Stephen K. Bannon’s nativist road map has led to dead ends in Britain and America, it’s tempting simply to see this as vindication — and take comfort in the shambolic predicament of the other side. But I’d argue that it’s a perfect moment to revisit the issues that fueled the populist revolt in the first place, and offer policies that actually help angry middle-class voters but don’t offer false hope that it’s possible to escape the realities of the 21st century.

Any party that wants to govern Britain must embrace the reality that “Leave” voters were right in their dissatisfaction with a feckless, over-bureaucratized E.U. system that’s better at delivering rules than results. “Brussels” has become a code word for a kind of elitist, we-know-better rule by unelected masters. The diktats of Brussels are as resented among working-class voters in France, Spain, Italy and the rest of Europe as in England. Every poll I’ve seen shows that broad dissatisfaction.

A new “Revote/Remain” campaign should begin with a pan-European alliance for reform — one that urges Britain to remain in a better “more perfect” union. The British Labour Party won’t be a plausible governing party, alas, as long as it’s led by the old-left relic, Jeremy Corbyn. He’s a big reason that the Conservative Party remains in power despite its current nervous breakdown.

What should the resurgent Democrats do on immigration after their midterm capture of the House? A modest proposal: Democrats should make clear that it’s not unethical or un-American to want a clear, enforceable border — and that not every migrant who wants to come to America can do so.

Many Trump voters think the Democrats are an elitist party captured by identity politics. Now, with the Republicans in disarray, is the Democrats’ moment to show that they can do what the GOP can’t — govern America fairly and equitably for all its citizens.

Twitter: @IgnatiusPost

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