President Donald Trump’s upcoming five-nation Asia tour is expected to strengthen ties with regional allies, but those gains could be diminished if the U.S. leader misses a key summit on the last leg of his trip.A major forum for political and economic cooperation among its 18 member countries, the annual East Asia Summit takes place on Nov. 13 to 14 in the Philippines this year. Trump will be in Manila on Nov. 13 but won’t attend the event, according to the U.S. State Department. Instead, Secretary of State Rex Tillerson will be representing the world’s largest economy at the summit’s plenary meeting on Nov. 14.Under former president Barack Obama, the East Asia Summit became a pillar in Washington’s Asia relations. In 2011, the U.S. acquired membership under Obama’s strategy of pivoting American foreign policy focus toward the Asia-Pacific region. Since then, the president attended every year except for 2013 when a U.S. government shutdown occurred.Trump’s Asia tour is the longest trip to the continent by a sitting U.S. president this millennium but missing the East Asia Summit is still a big deal for local leaders, experts say.