WASHINGTON -- The Obama campaign needs to convince middle-class voters that the president has a solid plan for improving the economy in a second term, argues Democratic über-strategist James Carville.

He could lose if he doesn't, Carville told The Huffington Post in a wide-ranging interview. He added that President Barack Obama doesn't dare talk about any first-term economic achievements, such as they are.

"When a politician says, 'You know, we've made real progress, the economy has made real progress,' people say, 'Well, he must be clueless' or 'He doesn't know what is going on with me,'" Carville said.

In his new book -- "It's the Middle Class, Stupid!" -- written with pollster Stan Greenberg, Carville recommends a relentless focus on the future of those voters. "Our argument has been, 'Don't talk about the last four years; talk about the next four years,'" he said.

But for the time being, the "Ragin' Cajun," who helped Bill Clinton win the White House twice, said Team Obama is right to focus on pushing Mitt Romney to disclose more than one year of his federal tax returns.

"What campaign wouldn't do what they're doing now?" Carville asked. "One year of the returns produced this kind of flood of stories. What will a bunch of years of returns do?"

Tuesday's flailing attack on the president by Romney surrogate John Sununu, former governor of New Hampshire, shows the tax return issue has unsettled the Romney camp, Carville said. "It's giving them fits."

Aside from raising the suspicion that the presumptive GOP presidential nominee is hiding something damaging, his refusal to make the returns public feeds a broader, damaging narrative, Carville contended.

"I would be very aggressive, saying that Romney believes a set of rules applies to him and then there is a set of rules for everybody else," said Carville. "He doesn't have to tell you about his taxes and his investments. He doesn't have to tell you about his plans for immigration. He doesn't have to tell you anything because he doesn't think you need to know. He doesn't really respect you. I think people are predisposed to believe that."

Still, there will come a time to move on from the tax issue, noted Carville, however fruitful it is now.

"The question is, When do you get out of it? Well, it's like when you give a speech. It's better to stop five minutes too soon."

"It's the Middle Class, Stupid!" is based not only on the authors' decades of experience in political campaigns, but on polls and focus groups across the country.

By rights and by history, the president should be way behind in the race, Carville said. He should have a job approval rating in the 20s, not nearly 50 percent.

But voters "don't think that there is a quick solution," said Carville. “The one thing Romney can't say is, 'You put me in there; we are going to create 300,000 jobs a month and incomes are going to go up by 6 percent a year.' They will not believe it."

Nor do they blame Obama alone for the economic decline since 2008, Carville contends. "What we say in the book is, 'Look, this is like someone with pneumonia getting hit with a truck. The voters were sick before it happened.'"

The president's number one imperative is to convince Americans that his health care law will actually slow the rise in the costs of getting sick, according to Carville.

"The president needs to say, 'I want to take the Affordable Care Act and really work on the 'affordable' part of it.' This is an act to build on, not to sit on. This is not an accomplishment; this is a work in progress."

"We've got to declare a national emergency," said Carville, his voice rising to the kind of pitch he used so often in the Clinton campaign's war room.

Middle-class voters, he said, are looking to government to control costs and make sure that one illness won't bankrupt them.

"If you knew there was something off the coast of California and it was going to invade the United States and it was certain to destroy the country, what would you say?" he asked. "You'd say, 'Sh*t! Waterboard somebody! Suspend the Constitution! Do something!'

"Well, it's here, and it's rising health care costs."

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