I'm surprised it's not obvious that Obama is leftist, but...
He supports raising taxes over cutting spending. He placed two leftist justices on the supreme court. He has cut military spending significantly. Supports gun control. Repealed don't ask don't tell. Supports gay marriage. Supports carbon taxes. Favors expanding social welfare programs. Favors debt and inflation over balanced budgets. Raised the minimum wage.
Conversely, issues where he falls on the right side of the spectrum are few and I would challenge someone to come up with a list.
Also, don't confuse his accomplishments with his political alignment. For example, I'm sure he would have created a single payer healthcare system if he could.