LIVERPOOL, England — Brexit is done, and Donald Trump, given the boot by U.S. voters, is angrily pacing the political sidelines. But the upsurge of rightwing populism that produced them both continues to roil transatlantic politics. Last Sunday, the far-right Brothers of Italy party, which has a fascist lineage, finished first in national elections. Its leader, Giorgia Meloni, will become Italy’s first female prime minister. She’s a socially conservative Christian who opposes immigration, abortion and LGBTQ rights. Although she’s toned down her Euroskepticism, Meloni also is an “Italy First” nationalist likely to align with illiberal regimes in Poland and Hungary....