President-elect Joe Biden introduced nominees for his national-security team during an event in Wilmington, Del., on Tuesday. Photo: Mark Makela/Getty Images European powers are looking to the incoming Biden administration to swiftly reduce nuclear tensions with Tehran but won’t press Washington to re-enter the 2015 nuclear accord with Iran quickly, according to senior diplomats. While European countries remain supportive of the 2015 nuclear deal, officials from France, Britain and Germany—countries that helped negotiate the accord—say a full return to the agreement might not be achievable or even desirable before Iran’s presidential elections in June. Amid…