I believe Kean has an excellent shot.
Menendez is viewed by many as a sleazy Hudson County machine politician. Believe it or not, even many democrat voters are looking for an alternative to the corruption that has tarred New Jersey politics. If the Republicans hammer home Menendez' questionable past, they can win. If they sissy out and let Menendez skate around his past, then they are in trouble.
Another factor that may hurt Menendez is his unapolgetic embrace of illegal immigrants. That stands to hurt him with Union voters and with plenty of average New Jerseyan's who have just about had it with illegals and the problems associated with them.