An incredible honor to receive the endorsement of a person I

have such tremendous respect for. Thank you, Sheldon! https://t.co/nW0N3OO4mw — Donald J. Trump (@realDonaldTrump) May 13, 2016

Sheldon Adelson, the billionaire CEO of the Las Vegas Sands casino group and longtime conservative political supporter, has endorsed Donald Trump for president and is urging House Speaker Paul Ryan and other reluctant Republicans to follow his lead.In an opinion piece published in Friday's Washington Post , Adelson writes:"I am endorsing Trump's bid for president and strongly encourage my fellow Republicans — especially our Republican elected officials, party loyalists and operatives, and those who provide important financial backing — to do the same.""The alternative to Trump being sworn in as the nation's 45th president is frightening … If Republicans do not come together in support of Trump, [President Barack] Obama will essentially be granted something the Constitution does not allow — a third term in the name of Hillary Clinton."Trump welcomed Adelson's endorsement on Twitter:Adelson added that Trump's experience as a business tycoon is a plus."He is a CEO success story that exemplifies the American spirit of determination, commitment to cause and business stewardship," Adelson writes."You may not like Trump's style or what he says on Twitter, but this country needs strong executive leadership more today than at almost any point in its history …"But some Republicans are sitting on the sidelines, threatening to stay home on Election Day or, worse, suggesting they will vote for Clinton. They must realize the stakes are too high for an outcome that will have a damaging impact on our country."Ryan has so far declined to back Trump despite his designation as the Republican Party's presumptive presidential nominee. Other noted Republicans like Mitt Romney have continued to blast the billionaire real-estate tycoon.