To use your vulgar slang definition of "tap"...

I wonder if Obama's tapped this ass yet.



The broader definition is simply to utilize.
 Quote:
7. To establish access to or a connection with: tapped a new market for inexpensive books.
8. To take advantage of; make use of: tapped voter anger to win the election.

Obama could combine forces with Hillary (as Romney has with McCain). But for a guy who campaigns on building bridges, he sure seems to have burned them with Hillary.

And similarly, regarding the MI and FL delegates, or any potential to join forces with Hillary when she reached out a few weeks ago. For a guy whose thing is reaching across the lines and working together, he seems to be pretty reluctant to work with anyone.