Senator John McCain’s future in the U.S. Senate may be a little less assured than previously thought.

A new Rasmussen Reports telephone survey of likely 2010 Republican Primary voters in Arizona finds the longtime incumbent in a virtual tie with potential challenger J.D. Hayworth. McCain earns 45% of the vote, while Hayworth picks up 43%.

Former Minuteman leader Chris Simcox gets four percent (4%) support, while two percent (2%) prefer some other candidate and seven percent (7%) are undecided.

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Hayworth, a conservative former U.S. congressman who now is a popular radio talk show host in Phoenix, is reportedly interested in the race but has not formally declared for it. He captures 59% of the male GOP vote, while McCain wins 58% of female voters.

Younger GOP voters like Hayworth more than their elders. McCain has a solid lead among the relatively small number of moderate and liberal Republicans in the state while Hayworth picks up a plurality (48%) of conservatives.

In late September, with Simcox his only likely opponent, 75% of GOP voters in the state said they expected McCain to win his party’s nomination for the Senate. But 61% also said McCain has lost touch with those in his own party.

Nationally, 74% of Republican voters say their party’s representatives in Congress have lost touch with GOP voters nationwide over the past several years.

By comparison, 59% of Republican voters say McCain’s 2008 vice presidential running mate, Sarah Palin, shares the values of most GOP voters throughout the nation. Palin is critical of the internal workings of last year’s campaign effort in her new book but continues to praise McCain. While campaign staffers have fired back at Palin, McCain, too, has been complimentary about her.

What makes the new findings even more unnerving for McCain, however, is that Simcox’s support is already a protest against the senator who has angered many conservatives in his home state with what they see as soft positions on illegal immigration and some other issues.

For McCain, the GOP Primary appears to be his biggest challenge since no major Democrats in the state have stepped forward yet to run against him.

Still, 74% of likely GOP Primary voters have at least a somewhat favorable opinion of McCain, including 35% who view him very favorably. Twenty-four percent (24%) regard him somewhat or very unfavorably.

Hayworth is viewed favorably by 67%, with 37% very favorable. Only 16% regard the ex-congressman somewhat or very unfavorably. But 16% don’t know enough about Hayworth to venture even a soft opinion of him.

Earlier polling showed that most Arizona voters said it was more important to pass immigration reform than health care reform. Most also believe Sheriff Joe Arpaio, an aggressive opponent of illegal immigration, has been good for the state’s image.

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