I have noted previously that Jeb’s lines of attack on Marco are pretty well limited to his lack of experience; immigration, Rubio’s greatest point of vulnerability, is off the table, as their positions are essentially similar. The other side of the coin is that Marco can only distinguish himself from Jeb by talking about his youth and his supposedly new ideas. When you combine the size of the stakes with minimal policy disagreements, you have a recipe for a campaign that is inevitably going to be intense and brutally personal; one way or the other, hard feelings will abound at its conclusion.
It is likely that the outcome of the Florida primary will ultimately determine the winner of this battle. It should be fascinating to watch.