This is not true. If Catholics were concerned with Christian charity they would object to the idea of giving tax money to the federal government for welfare. Churches can accomplish the task of reducing poverty far better than the government
Many of the folks in my parents generation still remember stories passed down to them by their parents and grandparents of the "No Irish need apply" signs that still graced many storefronts in cities well into the 1930's. The only way they got jobs then was to get off the boat, go to the nearest church and the Priest or a member of the parish would take them to the local Democratic party headquarters, and they would be given a low wage job through them. Therefore, they owed their very livelyhood to the Democratic party and were loyal as hell. Also remember to that there are two Democratic parties, the one that exists and the one older catholics thinks still exists. The party of FDR, Truman and JFK. That is my grandfathers democratic party, not the party of Hillary and Bill.
My grandfather used to tell me when I was younger, that the Republicans were the party of management and the Democrats the party of the working man. He could also never forgive the Republicans for the scare tactics used during the 1960 campaign, where GOP operatives went around telling all who would listen if JFK won the election the Pope would rule America. Many catholics are also union members, the problem with the GOP is still that alot of the GOP is anti-union, which I could never fathom because alot of union men and women are social conservatives. In closing, I hope i've shed a little light on it for you.