Former congressman J. D. Hayworth, a conservative advocate of stricter immigration enforcement, is set to challenge Senator John McCain for renomination in the Republican primary in Arizona.
McCain has been on pretty good behavior for the past year. It isn't clear whether this is due to anger at the rejection of the moderates he had courted over his career, preparation for this primary, or just a fluke.
Voters looking to refresh their memories on his record can see here:
Articles on John McCain
See also Michelle Malkin on who McCain's PAC is supporting:
Conservatives: Beware of McCain Regression Syndrome
Recent polls have shown McCain leading, but Hayworth with over 30%, which is pretty good at this point.