Incitement to violence can indeed cause violence. I don't think you have to look too far into history to find abundant examples of that. But I'm not sure that rhetoric which uses military terminology as metaphor has the same record, even among the fragile "unbalanced" that we are supposed to be so worried about. It's one of those things that people seem to accept as plausible, even without evidence, forgetting that people have access to books, movies, and music that are quite explicit in calls to violence.
That Obama and other Democrats have used more violent-sounding rhetoric is being amply demonstrated elsewhere, and I'm not going there. For the record, I have no objection to those comments as I browsed through them. If such martial or combative statements have any effect on inciting actual violence, it is lost in the sea of what people read or hear from other sources that they intentionally seek out, not that pop onto their TV screen when they were just minding their own business. People who are headed toward violence seek out fringe groups that are far more explicit in calling for it.
Where I can offer some expertise on the matter is the nature of those "unbalanced" people supposedly pushed over the edge by that rhetoric. Scanning my memory, I can identify: two of my patients who made national news for what appeared to be politically motivated attacks; two others who were peripherally involved with characters who made national news related to threatened political violence (one was on the outskirts of the Ed Brown tax-protesting saga in 2007, for example); and four patients who came to the attention of the Secret Service because of threats they made against political figures.
Seven of those eight were merely psychotic, with nothing political adding to the mix. The political angle was entirely accidental in two cases - being psychotic near a political figure. In the other five, the patient was attracted to the fame of the public figure as a way of getting their own paranoid message out to the world . The eighth was a personality disorder who had been a staffer on Bobby Kennedy's campaign and wanted to get back at some supervisor for entirely personal reasons.