Mr. Rove's speculation is deplorable. It may not represent a new low in American politics, but it betrays an individual who has initiated a stealth campaign against Hillary Clinton that relies on baseless and ugly health-related speculation, rather than engagement on ideas, experience, and leadership. It's all but a concession that the GOP cannot wage and win a fight on principles, vision, and policies. If, in fact that's the case, that's unfortunate, as a vibrant two-party system can add value while a one-party system can lead to stagnation in the long-run.
That such a remark was made so early--even before the 2014 Congressional electon has been held--suggests that Rove sees the GOP facing major competitiveness issues on a national basis. In other words, even as the GOP could win control of the Senate, his current thinking is that the GOP won't be able to translate those gains into a national election victory. Hence, he's thrown up a trial balloon to see if his ugly rumor gains traction. IMO, focusing on finding and developing a strong candidate, helping him or her articulate a clear and compelling message, and developing a robust electoral strategy would be far more productive than testing vicious personal attacks.
Sorry didn't see the warning