The skills that it takes to win nomination to office, or win an election, may in fact be the same skills necessary to do the job. People often think of elected office, especially executive office, as a position of command: the President gives orders, and they are carried out. But this is never actually true, even in a dictatorship, and far less in a democratic, constitutional republic. Getting an agenda carried out always requires the support of others, support which may be given or withheld. Executive position requires wheedling, dealing, negotiation, compromise, coalition-building.
Similarly, legislative action, if one is not going to be a simple back-bencher, passively voting yea or nay, requires the same skills. This skill set, often, happens to be the one which serves to get one elected, in the first place.
Effectiveness, of course, is not the only thing that is important. One’s place in history is determined by what one stands for and by how effective one is in carrying it forward. Ideology is important; so is getting the job done. Finding candidates with both these qualities is the ongoing challenge.