Chaffee voted against Alito's confirmation, so how can you say that a "loss" to the Dims even makes a difference? Chaffee opposes the President on many of the key issues, so I don't see how removing him from the Senate will make a significant difference when it counts.
If he could be counted on to remain a republican, one could argue that voting for him could allow the pubbies to keep control of the senate. The problem is that he cannot be counted on. He has stated that he would strongly consider switching parties if that would give control of the semate to the dumbs.
I've been criticized for saying that the worst republican is better than the best dem, but the one exception is Lincoln Chafee.
It was the vote against Alito that may have sealed Chaffee's fate, regardless. The sizable Italian population in Rhode Island was very upset over Chaffee's vote.
Even if Chaffee wins the Republican primary, he would likely be a dead duck in November anyway. (Not much difference between Chaffee and the Dem candidate, and a reason to vote against Chaffee due to his vote on Alito.)
Based on this I would argue that Laffey just may give Republicans a better chance of winning in November.