As Fox’s popularity grows among conservatives, the presence of four potentially serious Republican candidates as paid contributors is beginning to frustrate competitors of the network, figures within its own news division and rivals of what some GOP insiders have begun calling “the Fox candidates.”

With the exception of Mitt Romney, Fox now has deals with every major potential Republican presidential candidate not currently in elected office.

The matter is of no small consequence, since it’s uncertain how other news organizations can cover the early stages of the presidential race when some of the main GOP contenders are contractually forbidden to appear on any TV network besides Fox…

But it’s such a lucrative and powerful pulpit that Palin, Gingrich, Santorum and Huckabee have every reason to delay formal announcements and stay on contract for as long as they can.