(CNN) - The Republican Party's most recent presidential nominee has earned a primary challenge from the right on President's Day.
J.D. Hayworth, a former Arizona congressman and radio host, formally announced Monday that's he's challenging Republican John McCain for his U.S. Senate seat.
"You could say they are two John McCains. The one who campaigns like a conservative and the one who legislates like a liberal," said Hayworth at a news conference at his new campaign office in Phoenix.
Hayworth also announced Monday that another conservative candidate who was challenging McCain dropped out of the race and endorsed the former congressman. Hayworth's event kicked off what is scheduled to be a three-day, 10-stop campaign swing through the state.
Hayworth, who served for six terms in the House before losing his 2006 re-election bid, stepped down last month as host of his conservative talk radio program in Phoenix. While he says he respects McCain's service, he says McCain's been in Washington too long and isn't conservative enough.
"We all love and think the world of John and John's place in history is secure," the 51-year old Hayworth told CNN correspondent Casey Wian on Friday. "But John no longer represents the common sense conservative philosophy that most Arizonans share."
McCain, 73, is running for a fifth term in the Senate. The 2008 GOP presidential nominee served six years in the House before winning election to the Senate in 1986. McCain hasn't faced a difficult re-election since 1992.
Hayworth's Web page bills him as "The Consistent Conservative," challenging McCain on health care reform, the national debt and illegal immigration. And a Hayworth press release from Friday mentions that McCain "voted for the massive bank bailout bill in 2008, which included $150 billion in earmarks."
McCain, meanwhile, is in the middle of an eight-day campaign swing through the state.
Asked by a reporter if Hayworth was getting some grassroots conservative support, McCain said "I don't know what kind of support that Mr. Hayworth has. I haven't seen much so far, but maybe I missed it. And the voters in his district threw him out in 2006, in a heavy Republican district."
At a campaign event Monday in Tempe, Arizona, where he received the official backing of 31 mayors from across the state, McCain said "I intend to go out there and earn every single vote."
McCain also told CNN that "I'm tenacious, I fight and I love a good campaign."
Over the past few weeks, McCain has announced endorsements from top conservatives like Dick Armey of FreedomWorks and Grover Norquist, president of Americans for Tax Reform. Last month, McCain's 2008 running mate, former Alaska Governor Sarah Palin, announced that she would travel to Arizona to campaign with McCain in late March. Palin's popularity with voters on the right could help McCain with some Republican voters who question his commitment to conservative values and goals.
Sen. Scott Brown, whose victory in last month's special senate election in Massachusetts energized the GOP, has also said he'll stump with McCain early next month. And Arizona's Republican congressional delegation announced Wednesday that it will support the four-term senator.
"I think it's safe to say that McCain, coming out of the presidential race, was concerned about his possible re-election. I think he was expecting a challenge from the right," said Dan Nowicki, political reporter for the Arizona Republic.
McCain's was already facing a primary challenge from Chris Simcox, a co-founder of the Minuteman movement. Simcox announced his candidacy last April and then resigned from the volunteer organization, which tries to prevent illegal crossings of the U.S. border. McCain's past support of immigration reform legislation in Congress nearly derailed his presidential bid two years ago.
But Hayworth announced Monday that Simcox ended his bid for the GOP senate nomination, and endorsed Hayworth. Simcox's withdrawal could help Hayworth consolidate support on the right.
"When J.D. got into this race I thought long and hard about the decision I had to make, and it became obvious to me that the right thing to do was to remember the mission: Elect a consistent conservative to the United State Senate," said Simcox. "My friends, that is exactly what we are here to do. So it is with great pleasure that I stand with J.D. Hayworth and endorse his campaign."
Businessman Jim Deakin is also challenging McCain. The primary election is slated for August 24.
- CNN's Peter Hamby, Casey Wian and Chuck Conder contributed to this report.
Follow Paul Steinhauser on Twitter: @psteinhausercnn
Updated: 3:08 p.m.