… is from page 139 of my former professor Randy Holcombe’s 2018 book, Political Capitalism: How Economic and Political Power is Made and Maintained:
Ultimately, votes [in the legislature] are currency and the legislature has few enough members that they can keep track of IOUs and make sure that debts are paid. If they are not, legislators who renege on their debts will be excluded from future political exchange and therefore be rendered ineffective. The less principled a legislator is, the more successful that legislator can be in the political bargaining process. The political process itself contains a selection mechanism that favors unprincipled politicians over principled ones.