Just because it is rarely prosecuted, doesn't mean fraud does not occur. For you democrats, it is kinda like Clinton corruption - no doubt it exists, but it is rarely prosecuted. Good Article
Data from the 2012 election shows a large number of ineligible voters on the voter rolls. ....via the Pew Research Center:
•There were almost "24 million active voter registrations in the U.S. either invalid or inaccurate."
•Almost two million dead Americans were still on the active voting lists.
•12 million voter records were riddled with "incorrect addresses or other errors."
A number of congressional elections have been decided by voter fraud. The most notable of which was the election of Sen. Al Franken (D-MN) in 2008. Political scientist professors Jesse Richman and David Earnest noted that Franken only won by 312 votes, meaning that "votes cast by just 0.65 percent of Minnesota non-citizens could account for this margin." Noncitizens, the professors note, overwhelmingly supported Democrats that year. There were also 1,099 felons that voted in that race, all of whom were ineligible to do so.
Other examples of voter fraud deciding congressional elections from Fund's City Journal piece:
A 1996 INS investigation into alleged Motor Voter fraud in California's 46th congressional district discovered that "4,023 illegal voters possibly cast ballots in the disputed election between Republican Robert Dornan and Democrat Loretta Sanchez." Dornan lost by fewer than 1,000 votes. In 2002, Dean Gardner, a losing GOP candidate for California's state legislature, sent out a survey to 14,000 first-time voters. A total of 1,691 surveys came back. The results were startling: 76 people admitted that they weren't citizens but had voted, while 49 claimed not to have registered at their correct residence, as the law requires. Gardner lost by only 266 votes.
In the 2000 election, as the Missouri secretary of state later discovered, 56,000 St. Louis-area voters held multiple voter registrations. No one knows how much actual fraud took place, but it may have played a role in the Democratic defeats of incumbent Republican senator John Ashcroft, who lost his seat by 49,000 votes, and gubernatorial candidate Jim Talent, who lost by 21,000 votes.