Question

why does the president usually urge voters to elect members of the president's own political party to congress

Answer 1

Well think about it, the president's own political party would have many agreeing point of views and opinions right? So when the executive branch wants to pass a law (aka the president) than if the congress has lots of members of the President's own political party, than they would have an easy time getting laws passed, since they would agree on many of the president's bills, proposals, etc. Of course this doesn't happen all the time. In fact, I think there were more opposite political parties between the Legislative Branch and the Executive Branch in America. This is partly the reason why our government conducts their duties in a protracted matter and is also considered very inefficient by many members of the public.