WASHINGTON – Yes, Rick Perry says in his book that "by any measure, Social Security is a failure."

And the paperback version of Mitt Romney's book eliminates a line from the hardcover version that says of the Massachusetts health care plan, "We can accomplish the same thing for everyone in the country." Suddenly, campaign books matter.

Perry, the governor of Texas, wrote "Fed Up!" while Romney, the former Massachusetts governor, wrote "No Apology." The books have become ammunition in the Republican duel for the presidential nomination, as the two front-runners used each other's words as weapons during Thursday's debate.

The battle of the books is unusual in a presidential primary campaign.

Politicians traditionally use such tomes to add intellectual heft, detail their biographies to a public that barely knows them, and lay out their philosophies and promises.

But get too specific, and it could be trouble.

"Perry does say some things about Social Security that are harmful to him," said Bruce Buchanan, professor of government at the University of Texas. "He's going to have to literally renounce some of those views to be credible with a lot of people."

Romney, on the other hand, has been criticized sharply by some conservatives for his health care views. As governor, he signed into law the Massachusetts health care plan considered a model for the 2010 federal law that Republicans loathe. Romney explains today that each state should be free to craft its own health care plan, but imposing federal standards is misguided.

Perry on Thursday charged that Romney said his health care plan "was exactly what the American people needed, to have that Romneycare given to them as you had in Massachusetts. Then in your paperback, you took that line out."

"I stand by what I wrote," Romney said.

In the hardcover version of his book, Romney wrote, "From now on, no one in Massachusetts has to worry about losing his or her health insurance if there is a job change or a loss in income; everyone is insured and pays only what he or she can afford. ... We can accomplish the same thing for everyone in the country, and it can be done without letting government take over health care."

In the paperback edition, the words "We can accomplish the same thing for everyone in this country" are gone, and the book says: "And it was done without letting government take over health care."

Romney told CNN that he removed the line because the paperback version was updated and came out after the federal health care plan became law in March 2010. His campaign says the opposition to having government take over health care remains in both versions.

Social Security, though, has been the more incendiary issue at this month's three Republican debates.

Romney on Thursday charged Perry, who has toned down some of his criticism of Social Security lately, of "retreating" from the harsher views of "Fed Up!".

"Not an inch, sir," Perry insisted.

"Yeah, well, in that book, it says that Social Security was forced on the American people," Romney shot back. "It says that by any measure, Social Security was a failure."

Perry reiterated Thursday that current retirees, and those about to retire, "don't have anything in the world to worry about," citing a "solemn oath" the program will be there for them.

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