One of the problems in our primaries and caucus' is that so many of them are open. Whether or not you register a party affiliation you can vote in either party's caucus or primary. The problem with this is that a lot of partisans will go and vote for the opposite party's weakest candidate. They figure that this makes their own party candidate stronger.
Take this to the extreme. Suppose that all the Republicans voted for Dennis Kucinich in the primaries. Suppose that all the Democrats voted for Ron Paul. In the general election, it is Kucinich vs. Paul. Neither party liked either candidate. These were the two weakest nominees possible. But they won because of the people who perverted the process. Then we end up with Dennis Kucinich or Ron Paul as president. Either one would be disastrous.
I know people who do this. They are Democrats and go to the Republican primary to try to screw it up. They would never vote for the Republican in the general election.
I have not heard of any good solution to this problem.