TEL AVIV, Israel—U.S. Defense Secretary Lloyd Austin on Sunday declared an “enduring and ironclad” American commitment to Israel, reinforcing support at a tense time in Israeli politics and amid questions about the Biden administration’s efforts to revive nuclear negotiations with Israel’s archenemy, Iran. Austin’s first talks in Israel since he became Pentagon chief in January come as the United States seeks to leverage Middle East diplomatic progress made by the Trump administration, which brokered a deal normalizing relations between Israel and several Arab states. By coincidence or not, the defense secretary arrived as Iran reported that its underground Natanz nuclear facility lost power just hours after starting up new advanced centrifuges capable of enriching uranium faster. If Israel caused the blackout, it will further heighten tensions between Israel and the Iranian regime, already engaged in a shadow conflict across the wider Middle East. Iran called it an act of “nuclear …