It doesn't automatically buy, but it does influence and sometimes determines it, and not only in the US but in other representative democracies as well. Further on, the votes are by far not the only - or not necessarily the most - determining element in American politics, especially in foreign policies. Lobbies or even individual non-governmental policy makers do that with remarkable and ruthless expedience, and in this sense the US with its AIPAC or scoundrels like M. Klein is rather a particular case in the backdrop of other repr. democracies. It is plain obvious Jonathan Mann, Sergio Della Pergola and even most right-leaning political scientists on both sides of the pond. But the in the fear of repression or in order to "not provide an argument for the anti-Semites", they keep silence or stick to the verbal acrobatics based on the "only 2% of the Jews" in the US electorate. Whatever lie is not legitimate when there's no kid around screaming the king's naked.
Palestinians call general strike in J'lem Old City over police conduct, settler violence (Haaretz)
from the article: So few Jews, so much clout in U.S. polls