After coming within a few million votes of the presidency, John McCain is suddenly facing the toughest re-election fight of his nearly 24-year Senate career.

Former Rep. J.D. Hayworth is slated Monday to kick off his campaign for the U.S. Senate with a three-day, 10-city tour across Arizona. Mr. Hayworth, 51, a favorite of the insurgent "tea party" movement and a border-security hawk, is running as a younger, brasher, more conservative alternative to Mr. McCain, who turns 74 a few days after the Republican Party's Aug. 24 primary.

"I have a lot of respect for John McCain - he's served this nation admirably - but this is about policy," Mr. Hayworth said in a telephone interview. "Although he describes himself as a maverick, he's really a moderate. So many people have reached out to me and said, 'Please, we need a conservative senator.'"....