Kentucky

[Verily]

Bunning will be easier to defeat than to take an open seat, so he shouldn't be goading him into retirement.

It may be an attempt to appeal to Bunning's wily side. If Mongiardo taunts Bunning enough, it's more likely that the old loony tries to run for reelection.

[Verily]

He recently compromised on a big one.  And this isn't an ordinary primary, this is trying to unseat an incumbent who is solidly conservative and in Kentucky

Think Northup v Fletcher, only Bunning isn't even corrupt, just senile. McConnell's faction in Kentucky GOP politics is hated by the voters, at least in the primaries (and the 2008 Senate election results suggest it isn't too popular in general elections, either).