Those questions, though, aren’t going away, and neither are the ones about the judgment of Mr. Romney and Mr. Ryan in drawing ever closer to a man whose business background should lead them to back away — fast. By not repudiating Mr. Adelson’s vow to spend as much as $100 million on their behalf, the two candidates seem more eager to keep the “super PAC” dollars flowing than to preserve the integrity of their campaign.
      
The issues swirling about Mr. Adelson’s business practices are not new and can hardly come as a surprise to the Romney campaign. Last year, his company, the Las Vegas Sands Corporation, announced that it was under investigation by the Justice Department and the Securities and Exchange Commission for possible violations of the Foreign Corrupt Practices Act — specifically, that it bribed Chinese officials for help in expanding its casino empire in Macau. Later, the F.B.I. became involved, and even Chinese regulators looked askance at the company’s conduct, fining it $1.6 million for violating foreign exchange rules, The Times reported on Monday.
      
Then there’s an unrelated investigation by the United States attorney’s office in Los Angeles into whether the Sands Corporation violated federal money-laundering laws by accepting millions from high-rolling gamblers accused of drug trafficking and embezzlement. The Wall Street Journal reported earlier this month that federal authorities are examining whether the casino should have reported the suspicious funds to the government. Instead, the company accepted $100 million from one of the gamblers and gave him free hotel rooms, plane rides and large lines of credit.
      
The company has denied all allegations of improper behavior. But, since Mr. Adelson’s financial future is riding on the outcome of these federal investigations, it is legitimate to ask whether he has motivation for supporting the Republican ticket so lavishly, beyond his sharp disagreement with the Obama administration’s position on the Israeli-Palestinian peace process. Mr. Adelson has certainly not hesitated to throw around his weight and wealth with Republicans before.
      
In 2001, when China was making a pitch to hold the Olympics, it was worried about a resolution pending in the House that would oppose the bid because of its “abominable human rights record.” To curry favor with China, Mr. Adelson called Tom DeLay, then the House majority whip — and another recipient of Mr. Adelson’s campaign generosity — and urged him to block the resolution, according to a court deposition by William Weidner, then the president of Sands. Mr. DeLay quickly promised the bill would never see the light of day, and he was true to his word.
      
The next day, a Chinese vice premier promised Mr. Adelson an endless line of gamblers to the Macau casino.
      
A careful presidential campaign would put distance between itself and a businessman like Mr. Adelson. Instead, this one is cultivating him. Mr. Romney recently met with him in Israel, and Mr. Ryan this week paid homage to him and other big donors in a private casino for high-rollers on the 36th floor of Mr. Adelson’s Venetian hotel. By allowing Mr. Adelson to have such an outsize role in their race, the candidates themselves are placing a very risky bet.