It's fair to say that John McCain has said that some measure of U.S. troops might stay in Iraq for as long as 100 years. Or something like that.
It's not fair to say that McCain wants to war to continue for 100 years.
There is a school of thought that holds that the presence of troops contributes to and feeds the instability and so, it may well be fair to link the presence of troops to a perpetual state of war. But that's an argument one has to make and not simply assume into evidence.
When, in Derry, New Hampshire, McCain uttered the phrase "make it 100," he was comparing the U.S. presence in Iraq to the U.S. presence in South Korea.
Clearly, this comparison implies a healthy amount of troops in the region and continued high-level military cooperation and self-defense treaties. That should be enough for Democrats. "100 years" -- even in the correct context -- is just one of those phrases that politicians were invented to exploit.
Instead, Democrats imply that McCain wants to keep US troops in Iraq for 100 years under the same conditions they're fighting right now.
Which is simply not what McCain said. McCain explicitly said that US presence in Iraq long-term would be predicated on the absence of violence and on the establishment of stability in the region.