If he sends armed forces, Obama will lose a lot of support from illegal aliens, and anyone who loves illegal aliens. Even if he does send troops, the Republicans will still be mad at him for some other reason, and then he won't have the support of anyone. Go figure.
It's very basic politics; he's trying to reassure his next election. Then again, there's a whole boatload of inner politics that would make anyone vomit, so for all we know, this is a distraction from whatever the real issues are.