The fifth Republican presidential debate will be held tonight at a casino owned by one of the biggest donors to the Republican party — and he is yet to endorse a candidate.

The debate will be held at the Venetian Hotel in Las Vegas, owned by businessman and megadonor Sheldon Adelson. Adelson spent $93 million (just to groups who disclose their donors) on the 2012 election, including $30 million for Mitt Romney and $23 million for Karl Rove’s super PAC American Crossroads.

That’s made Adelson a bit more cautious this time around. Matt Brooks, the director of the Republican Jewish Coalition and friend of Adelson, told Bloomberg that Adelson’s “strategy is different this time. He is taking a wait-and-see approach.” That was in April, and Adelson still hasn’t endorsed a candidate. Some say Rubio might edge the others out in the “Adelson primary,” but Adelson’s wife, Miriam, has reportedly become more interested in Ted Cruz.

Despite these rumors, the only candidates who have so far received any money from Adelson are Rubio and Lindsey Graham, who is lagging in the polls. According to an invite obtained by Political Party Time, Adelson was a co-chair of a fundraiser for Lindsey Graham’s Security Through Strength PAC in March, meaning he donated the federal maximum of $2,700. Graham polls at less than one percent nationally; but Adelson is used to getting a low return on investment: Mitt Romney, of course, lost the presidential election, and American Crossroads won only 1.29 percent of its races.

Adelson’s step-daughters, Sivan Ochshorn and Yasmin Lukatz, also have a history of writing big checks to GOP candidates and causes.

In 2014, though, a better year for the GOP, Adelson’s bets paid off as his chosen candidates for U.S. Senate went on to win their respective elections. These included Sens. Joni Ernst, Iowa, Tom Cotton, Ark., Cory Gardner, Colo., Bill Cassidy, La., and Dan Sullivan, Alaska.

And personal giving isn’t the only way Adelson’s network boosts the GOP. According to data from OpenSecrets.org, since 2012, the Las Vegas Sands Corporation — which is controlled by Adelson and which owns the Venetian — has donated about $650,000 almost exclusively to Republican congressional candidates.

Winning the Adelson primary hinges largely on a candidate’s support for Israel: New York Magazine noted that “Adelson’s support for the Jewish state is so intense that he opposes American efforts to broker a two-state solution to the Israeli-Palestinian conflict, arguing that the Palestinians are ‘an invented people’ whose ‘purpose … is to destroy Israel.’” In 2014, New Jersey Gov. Chris Christie met with and apologized to Adelson for using the term “occupied territories” to refer to Palestine.

The decision to host the debate at Adelson’s casino has been somewhat controversial among the Republican campaigns: Last month, Politico reported that several campaigns were concerned that Adelson’s extra bloc of allocated tickets meant he would try to stack the crowd in his favor. Adelson still hasn’t endorsed a candidate, so it seems like that’s less likely now.

One explanation for his lack of public endorsement could be the use of 501(c)(4) nonprofits, dark money groups that do not have to disclose their donors. This was noted by Justin Miller at the American Prospect, who reports that “GOP insiders have said that he’s given more and more to prominent dark-money groups rather than to super PACs that must disclose donors.” Rubio, for example, is being supported by a dark money group that has spent $8.5 million on ads for him. The move by Rubio’s allies to embrace dark money is unprecedented for a candidate in presidential politics.

So maybe the Adelson primary has already been won — we just might never know it.