How do political parties act as "bonding agents" between themselves and voters?

In what way do political parties act as "bonding agents" between themselves and the voting public? ... It takes 270 electoral votes to win a presidential election.

Explanation:

In politics, a political party acts as a "bonding agent", to ensure the good performance of its candidates and officeholders. IN choosing its candidates, the party tries to make sure that they are men and women who are both qualified and of good character.