It is unlikely any country will ever again "declare war" on any other country. Today's conflicts are seldom about country to country invasions. Even Iraq invading Kuwait was dealt with as a UN matter:

"On August 3, 1990, the UN Security Council passed Resolution 660 condemning the Iraqi invasion of Kuwait and demanding that Iraq unconditionally withdraw all forces deployed in Kuwait.[39] After a series of failed negotiations between major world powers and Iraq, the United States-led coalition forces launched a massive military assault on Iraq and Iraqi forces stationed in Kuwait in mid January 1991."

I fear Obama would get MORE criticism for not helping countries with naughty dictators! Indeed, it is happening now regarding Libya.