All seven incumbents who ran for re-election, none of whom faced viable challengers, were returned to Congress.

Republicans failed to put forward a viable challenger during any of Ford's re-election bids.

No one else is within 20 points, and while we're not yet ready to declare these two the only viable challengers for the Sprint Cup, it's getting awfully close.

GameTrailers stated that "another viable challenger has stepped onto the stage."

Earlier, McCloskey had led an effort to find a viable primary challenger to Pombo.

Other examples of open-source software include Linux, which has emerged as the most viable challenger to Microsoft's Windows operating system for corporate customers.

With no viable political challengers and a political system in place that blocks their emergence, Mr. Putin faces no serious threat to his political authority.

"It's unfair that the press keeps saying there are no viable challengers," said Mr. Payne, who is considered the Mayor's chief rival.

Politicians have said he has to establish quickly that he will be a viable challenger.

Besigye, viewed as the only viable challenger to Museveni, was one of six candidates, during a campaign that contained much recrimination and bitterness.