Here is video of President Obama at the "Health Care Summit" saying he did not count his time in the division of time between Democrats and Republicans because "I'm the President." He said it as if he is some impartial observer. In fact, Democrats spoke about twice as much as Republicans when you count Obama's time. The last time I looked Obama is a Democrat!
To dominate the time, what Obama is doing is that he comments after a Democrat speaks, and again after a Republican speaks. In effect, the Republicans are being dominated "2 to 1", if not in actual minutes in the end, then by Obama's commenting on every comment.