In the United States, the couple was a key source of support for the Republican Jewish Coalition, which remained a close ally of Mr. Trump throughout the course of his turbulent presidency. The Adelsons were among those who helped persuade Mr. Trump to lean into a hard-line pro-Israel stance, which led to his decision in 2017 to relocate the American embassy to Jerusalem from Tel Aviv — a move that incensed Palestinians and led to unrest across the Middle East after it was announced.
The couple was seated in the front row for the ribbon-cutting ceremony commemorating the move in May 2018. That day, Dr. Adelson described Mr. Trump as “the Truman of our time” in an extraordinary front-page editorial in The Las Vegas Review-Journal, which she and her husband purchased in 2016 and have used to promote their domestic and foreign policy interests.
American conservatives were left wondering what his absence would mean for the relationship between Israel and the United States going forward, as Mr. Biden is expected to adopt a more moderating approach. “We have been unabashedly staunch allies of Israel,” said Bradley A. Blakeman, a Republican consultant who served in the George W. Bush administration. “My fear is that we will go back to playing both sides against the middle.”
Mr. Adelson’s huge spending changed the contours of the battles for the Senate and House in recent years, as well as past Republican presidential nominating contests. In 2012, he funded a super PAC supporting Newt Gingrich that bloodied the eventual nominee, Mitt Romney, and gave Mr. Gingrich’s often quixotic campaign a longer shelf life than many expected it to have. But in the general election, the Adelsons invested millions more in another super PAC that aimed to help Mr. Romney defeat President Barack Obama.
For years, top Republicans sought Mr. Adelson’s approval and cash. In the 2016 presidential primary, Mr. Trump attacked his fellow Republicans for pursuing Mr. Adelson, in particular Senator Marco Rubio of Florida, who he said would be the casino magnate’s “perfect little puppet.”
But their relationship with Mr. Trump evolved over time. Once Mr. Trump became the apparent Republican nominee and the party started to unify around his renegade candidacy, Mr. Adelson agreed to back him and offered him some advice by urging him to express more humility as a candidate.
After Mr. Trump’s election in 2016, Dr. Adelson wept tears of joy over his promises to support Israel. At a meeting in January 2017 at Trump Tower in which Mr. Trump promised he would move the embassy to Jerusalem, she exclaimed, “I can’t believe it!” and hugged the president-elect, according to one person who witnessed the exchange.
In November 2018, Mr. Trump bestowed the Presidential Medal of Freedom on Dr. Adelson. The Adelsons had just spent more than $120 million helping Republicans in the midterms.
David M. Halbfinger contributed reporting from Jerusalem.