The biggest interview on television last week, with the Senate candidate Rand Paul, happened at 9 p.m. But regrettably for CNN’s Larry King, who used to rule that time slot by wooing newsmakers, the interview was booked by his higher-rated competitor, MSNBC’s Rachel Maddow.

Next week will be Mr. King’s 25th year on CNN, but these are hard days for the host, and not just because he is being beaten in ratings and bookings.

Although still the linchpin of CNN’s lineup, he has come to embody an enormous problem facing the cable news channel. How can he and CNN compete in prime time when viewers seem to crave partisan political programs and when prominent guests — the lifeblood of Mr. King’s show — would rather burnish their images on other channels?

So far, CNN cannot compete. “Larry King Live” is now struggling in the ratings, as is CNN as a whole. The ratings for the new “John King, USA” political show at 7 p.m. have been disappointing, and Campbell Brown announced last week that she was quitting her 8 p.m. show after concluding that her newscast could not compete with the bombastic opinion-oriented shows on Fox News and MSNBC.