Why did Ted Kennedy challenge Carter in 1980?

[TomC]

Also, don't forget, during the primaries, the Iranian hostage thing was a pretty new crisis, and I'd argue the country rallied around the President in this time, hurting Kennedy. But by the time the general rolled around, and the problem hadn't been resolved, voters were weary of the crisis and blamed Carter.

[TomC]

In December of 1979, Reagan was not the front runner.

Nope!

In fact, a poll in January 1980 showed Carter waaaaaay up on Reagan, by about 30 points.

I believe Carter was ahead for most of the campaign. That's where "October Surprise" comes from- Reagan's surge ahead a month before the election.