Defense Secretary Lloyd Austin said Saturday that the wars raging in the Middle East and Europe, coupled with increasingly brazen “bullying” by China, have underscored the need for robust U.S. leadership on the global stage. “Only one country on Earth can provide the kind of leadership that this moment demands…and that’s the United States of America,” said Mr. Austin, who warned that global security crises will only worsen if Washington chooses isolation over engagement. “We’re living through challenging times,” the Democrat-appointed defense secretary said in the keynote address at the 10th annual Reagan National Defense Forum — a bipartisan event...