Tonight's presidential debate will have a global audience, high stakes and plenty of political drama as President Barack Obama and Mitt Romney square off for the first time.

What it won't have is a third candidate. The sponsor of tonight's showdown - the nonpartisan Commission on Presidential Debates - ruled that Libertarian Party candidate Gary Johnson will not be allowed to participate.

The commission said Johnson failed to meet its threshold of receiving at least 15 percent of the vote in a major polls. Johnson filed a lawsuit to contest the decision, but won't be on stage at tonight's event in Denver.

That's drawn the protest of at least two of the debate's corporate sponsors, Philips Electronics and the YMCA, who said they were pulling their support because of Johnson's exclusion.

The last time an independent candidate was allowed to participate in a debate with nominees from the two major parties was in 1992, when Ross Perot joined the stage with President George H.W. Bush and Bill Clinton.

Johnson said today his campaign will provide live commentary during the debate via Twitter and other social media. But the former New Mexico governor made it clear that he's not happy to be shut out of tonight's event.

"Someone has to stand up and call this what it isa rigged system designed entirely to protect and perpetuate the two-party duopoly," Johnson spokesman Ron Nielson told US News and World Report. "That someone will be the Johnson campaign."

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Libertarian candidate Gary Johnson shut out of tonight's debate, claims 'system is rigged'