Las Vegas casino tycoon Sheldon Adelson upped his ante in former House Speaker Newt Gingrich's unregulated issues-advocacy group in August, with a $750,000 donation that helped propel the organization to the No. 2 fundraising spot among so-called 527 political groups this election season.

Amid new signs that its signature “Drill Here. Drill Now. Pay Less.” campaign was reaping success on Capitol Hill, American Solutions for Winning the Future reported a total $1.9 million in contributions for August, its second-best fundraising month. (Its best was a $2.1 million showing in June, when the group rolled out its campaign to end the 27-year-old U.S. moratorium on offshore drilling, and Republican presidential candidate John McCain took up the cause.)

Senate Democratic leaders now indicate they will likely allow the drilling ban to expire on Sept. 30, rather than force a confrontation with conservatives who, cheered on by Gingrich and his group, threatened a budget showdown. A bipartisan group of Senate moderates, the so-called “Gang of 20,” had come up with a compromise to open only some offshore areas to drilling, but they have decided against introducing their legislation in the politically charged pre-election atmosphere.

When added to the Center for Responsive Politics’ pre-August tally for the group, the new contributions bring American Solutions’ total haul to more than $16 million this election season. Only the Service Employees International Union’s issues-advocacy arm has raised more; SEIU has voluntarily filed with the Federal Election Commission as a campaign committee, making it subject to donation limits.

However, American Solutions faces no such restrictions — one reason Adelson, chairman of Las Vegas Sands, was able to further secure his position as the group’s leading donor, with a total of $5.4 million in contributions. As the Center reported earlier, American Solutions bills itself as a “new, innovative, and nonpartisan” organization, but Gingrich says he’s personally working to help McCain. And the group’s leading donors are GOP stalwarts, including Adelson, who is one of the elite Trailblazers who have raised in excess of $100,000 for McCain and the Republican Party.

In August, about 50 percent of American Solutions’ contributions came from Adelson and six other donors who have given thousands to GOP candidates, PACs, or committees this election season. Checks for $25,000 each came from Virginia real estate developer Guiseppe Cecchi; Larry Franklin, chief executive of the Harte-Hanks marketing firm, San Antonio; Houston Harte, vice chairman of Harte-Hanks; and Ken Langone of New York, a venture capitalist, co-founder of Home Depot and former New York Stock Exchange director. Florida real estate developer Mel Sembler, a long-time GOP fundraiser, doubled his giving to American Solutions with a $10,000 donation in August. The only big donor last month with a bipartisan profile was Jim France, executive vice president for NASCAR in Daytona Beach, who gave the Gingrich group $8,800 (for a total of $17,600 this year). France gave to the Democratic Senatorial Campaign Committee and to House Ways and Means Committee Chairman Charlie Rangel, and contributed to former New York Mayor Rudolph Giuliani’s presidential bid as well. .

American Solutions is gearing up for its big Solutions Day event on Sept. 27 in Atlanta, which it is billing as “a national forum on real change and real solutions for energy, health, education, and the economy,” and for which Gingrich has said the goal will be “setting the stage for the October finale of the presidential and congressional and gubernatorial and local campaigns.” With the offshore drilling battle all but won, it’s not clear whether American Solutions will shift to a new issues focus in the final weeks of the campaign. In recent days, Gingrich has been vocal in his opposition to Treasury Secretary Henry Paulson’s $700 billion Wall Street bailout plan, which he has blasted as “profoundly wrong.”

Matthew Lewis contributed to this report.