Vietnam’s leadership this year of a Southeast Asian negotiating bloc has opened a door to bolster its defense against longtime rival China through stronger relations with the West, experts say.The Quadrilateral Security Dialogue, or Quad, a U.S.-led grouping that also includes Australia, India and Japan, invited Vietnam to join talks on COVID-19 and economic impacts in March, and its members have conferred with Vietnamese officials regularly since then.  U.S. Secretary of State Michael Pompeo finished his five-nation Asia visit with a stop in Vietnam Friday.  He praised the host country’s “sovereignty” when he met Friday with Foreign Minister Pham Binh Minh in Hanoi and said he looked forward to further improvement in relations.  FILE – A ship (top) of the Chinese Coast Guard is seen near a ship of the Vietnam Marine Guard in the South China Sea, about 210 km (130 miles) off shore of Vietnam, May 14, 2014The two sides periodically ram each other’s boats and try to keep each other away from undersea energy reserves — as China uses technological and military advantages to occupy tiny islets.    The two communist neighbors often make up after these incidents but never settle them. They had already sparred on and off for centuries over territory, culminating in a war in the 1970s.   Quad connections “will give Vietnam a solid regional ‘coalition’ to work on China with,” said Yun Sun, East Asia Program senior associate at the Stimson Center in Washington. “For a Vietnam that has been resisting China alone for centuries, to have those solid partners will improve Vietnam’s leverage and position,” she said.   The Quad was launched 13 years ago. It’s seen as a counterweight to Chinese expansion, from the Sino-Indian border to the South China Sea. New Zealand and South Korea joined Vietnam for Quad talks this year about COVID-19.   China will “think the worst” of Vietnam’s Quad role, Thayer said.     Vietnam has hardly forgotten ASEAN or forsaken China, though. As ASEAN readies for a leadership summit November 11-15, Vietnam has a chance to help the members clinch a free-trade agreement involving China. China is already an economic benefactor for much of Southeast Asia, and Vietnam counted China last year as its No. 2 trading partner, after the United States.   FILE – Container trucks are seen while waiting for cross the border at Huu Nghi border gate connecting with China, in Lang Son province, Vietnam, Feb. 20, 2020.A breakthrough this year in the Regional Comprehensive Economic Partnership deal after nine years of discussion would make Vietnam “look good” by helping so many economies, said Rajiv Biswas, senior regional economist with IHS Markit, a London-based market analysis firm. The 15 would-be partnership countries make up almost 30% of the global gross domestic product.   “Because these things have been under conversation for quite a few years, if they can pull it off under their chairmanship then it looks good that they were the ones who were able to bring it over the line,” Biswas said.