There's also the fact most secular American Jews are liberal and for them liberalism is their religion. Its replaced Judaism and they do not think for the most part, first and foremost as Jews. They think as liberals and that explains the continued voting loyalty of most American Jews to the Democratic Party, even when it runs counter to Jewish interests in both continued Jewish survival and in Israel's welfare.
(Go Israel, Go! Slap 'Em Down Hezbullies.)
Indeed, the Democratic Party is THE
secularist party. So, that secular Jews find a political home there is hardly surprising. If one no longer trusts G-d, then one builds a 'god' of the state.