Obama, somewhat famously now, seems to have tried to meddle (without success) in the New York gubernatorial election and perhaps the Colorado senatorial nomination contest as well to similar result.
The Republicans don't seem to be fairing much better:
The push by Washington Republicans to identify preferred Senate candidates has stirred resentment and prompted competition from those not impressed by the Washington seal of approval.
In this era of strong congressional parties, it's particularly important to remember the limits that each party faces in simply making itself up.