I read the whole article (which is from late March '07, which may be significant, coming as the GOP candidates were announcing). It never says that McCain was considering switching over to the Democrats, only that he was considering becoming an independent.

McCain's reasons were supposed to be: "...McCain at that time was frustrated with the Bush administration as a result of his loss to George W. Bush in the 2000 Republican primary."...'He pointed out that few, if any, of McCain’s people were hired by the Bush administration. “John didn’t think that was right,” Daschle wrote, “that his staff should be penalized like that.”'

Given the context that McCain was pretty pissed-off at Bush and the GOP machine that worked to defeat him, often with dirty tricks, you might consider that McCain's decision to stay with the GOP is a case of the glass being half-full. It's easy to remain loyal in good times, but McCain remained loyal through and after some pretty bad times. His Party treated him badly, but he hung in there.

Like I said at the beginning, an article published in March '07 is kind of suspicious. It may well have been a political dirty trick to discredit McCain among Republicans...which suggests that Democrats see McCain as a serious challenger in '08.

A lot of Republican voters are vulnerable to persuasion by that kind of tactic because of the fierce partisanship that demands ideological purity. Look at how the primary candidates try to smear each other with the "Liberal" label. The tactic would be less likely to work if you'd lighten up a little and take into account other factors, like character, instead of just narrow ideological focus.

As Ronald Reagan is reported to have said, "Would you rather have 50% of what you want, or 100% of nothing?"