PARIS — Europe’s security pledges to Ukraine face a potential expiration date. French President Emmanuel Macron and British Prime Minister Keir Starmer are pressing ahead with plans to guarantee Ukraine’s postwar security — including the possible deployment of French and British troops as peacekeepers. But with right-wing populist leaders rising fast in both countries, those commitments could soon come under strain. Jordan Bardella of the National Rally is the front-runner to win France’s