Gabriel Bouys, Getty Images
Arizona Sen. John McCain and former Massachusetts Gov. Mitt Romney appear together during a GOP presidential candidates debate on Jan. 30.

WASHINGTON — It always sounded innocuous enough, tucked into the adjectives Mitt Romney would rattle off when he described the qualities for the next president.

Wisdom, optimism and the right temperament, said the former Republican presidential candidate.

There was no doubt whom Romney was referring to — rival and likely GOP nominee John McCain, whose short-fuse temper is widely known, especially among his Senate colleagues.

The dig that McCain lacks the comportment to be commander in chief was part of the playbook that Romney used in his unsuccessful bid to secure the Republican nomination. Now it provides a piece of the playbook for either Democratic Sen. Hillary Rodham Clinton or Sen. Barack Obama in a general election campaign against the four-term Arizona senator.

Among the weaknesses that Romney criticized:

• McCain's admission that he was better versed in foreign affairs and military matters than economic issues.

• McCain's flip-flops both philosophically and on specific issues.

• McCain's alignment with Democrats on taxes, illegal immigration, campaign finance and environmental issues.

Romney stopped short of labeling McCain a liberal, but he said McCain's history of agreements with Democrats would leave voters little more than intangibles with which to distinguish between the Democratic and Republican nominees.

While he never defined those intangibles, Romney suggested McCain would be a liability in a race in which the 71-year-old would be trying to become the oldest person ever elected president, while Clinton was trying to become the first female president and Obama, the first black.

Romney himself never attacked McCain's age or temperament directly, but his campaign aides were not shy about highlighting McCain's volcanic temper.

"Choosing to ignore substance and relevant issues, the McCain way has always been to attack opponents in a personal manner," read a Jan. 5 e-mail from Romney press secretary Kevin Madden.

McCain has said such outbursts were understandable as he fought pork-barrel spending or clashed passionately with his rivals.

As polls showed voters more concerned about the economy than other issues, Romney argued that a key difference between him and McCain was in their financial ability.

McCain told reporters last November that among the qualities he might seek in a running mate is someone with a firm grasp of economics. "You also look for people who maybe have talents you don't, or experience or knowledge you don't, as well," the senator said.

In December, McCain again told reporters: "The issue of economics is not something I've understood as well as I should."

Romney, who made millions as a venture capitalist, pounded McCain on the stump for the remarks. He told delegates to the West Virginia Republican State Convention in his final campaign speech: "One of the guys running for president the other day said the economy is not his strong suit; well, it is my strong suit."

Romney also questioned McCain's conservative credentials and political reliability. In 2000, McCain branded televangelists Jerry Falwell and Pat Robertson "agents of intolerance." Six years later, McCain visited Falwell's Liberty University as part of his outreach to Christian conservatives.

"I could regale you with all of the positions of his that have changed; I think you know a lot of them," Romney told reporters in West Virginia.

Romney often brought up McCain's two votes against President Bush's tax cuts, which the Arizona senator now wants to make permanent.

That criticism underscored a deeper concern Romney had about McCain.

He pointed out that McCain departed from conservative orthodoxy to join with Sen. Russell Feingold, a liberal Democrat, in writing campaign finance restrictions, with liberal lion Sen. Edward Kennedy on immigration proposals and with moderate Democrat-turned-Independent Joe Leiberman on greenhouse gas emission legislation.

"When Republicans act like Democrats, America loses," he would say on the stump and in campaign literature.

Given that Romney didn't prevail over McCain, Democrats are sure to supplement any attacks they borrow from Romney attacks with fierce criticism of one position McCain and Romney shared: support for Bush's war in Iraq.

McCain himself has predicted that will be a major general election issue, and Romney said he was withdrawing for fear of aiding a Democratic victory that would alter the war policy.