If he had any evidence ...
If Obama had any evidence the U.S. Chamber of Commerce was using foreign money to fund their ads, we'd have heard about it weeks ago. Using funds from foreign nationals for political purposes is still a federal crime. No matter what Obama would like you to believe, Citizens United didn't change that policy. As such, if he had even the smallest shred of evidence that the Chamber was actually funding any political ads with foreign money, his buddies in the House would be holding hearings faster than you can say "I can see November from my house." Waxman the Intimidator would have the nostrils of doom in full flair and no extravagance would be spared in the ensuing media flaying. The Justice Department would have launched an investigation. Instead, Obama has zero evidence to support these baseless accusations. This is the last ditch effort to scare what remains of his base into voting.
The real story here is that Obama's presidency and his policies have been so disastrous for our nation that no Democrat has been able to run on his agenda. We've seen more money spent by Democrats hyping their vote against Obamacare than has been spent on ads supporting a vote for that toxic legislation. The Democrats faring best fall into two categories. Those whose voting districts are a liberal swamp that won't vote R until hell freezes over, and those who have managed to run far far away from the president and successfully campaign against his agenda—in other words, running as Republicans.