What Motive Does a President Have to Endorse a Candidate

What motive does a president have to endorse a candidate running for Congress within his or her own political party?

A) Supporting a candidate running for Congress will help that candidate get onto a committee.
B) Endorsing a congressional candidate boosts the president's public perception.
C) Doing so gives the president leverage to ask for support once the candidate is in Congress.
D) Endorsing a candidate running for Congress is simply part of the president's duty as party leader.