A newly combative Barack Obama on Wednesday warned the struggling voters of the American Midwest, whose ballots could decide the presidential race, that Mitt Romney would betray them if elected and must not be trusted.Opening a "48-hour, fly-around marathon extravaganza" of crucial states with his most aggressive speech of the campaign so far, the president urged Iowa not to catch "Romnesia" and forget the radical plans his Republican challenger now plays down. "We joke," he told 3,500 supporters at a soggy fairground, with the same spikiness he displayed in this week's final televised debate. "But all of this speaks to something important: trust. There's no more serious issue on a presidential campaign than trust. Trust matters." "You know me, Iowa," he told the state that propelled him to the White House with a shock party caucus win in 2008. He added that while Mr Romney flip-flopped, Mr Obama was "the same guy". Onstage the president, who leads Iowa polls by two percentage points, brandished the 20-page manifesto he has published late in the campaign to counter charges that he has no second term agenda.He was followed into the state – a vast expanse of corn fields bigger than England, with a population of just three million – by Mr Romney, who said the glossy pamphlet disclosed "no new plans". Accusing Mr Obama of ditching "change" to become the "president of status quo", he said in Cedar Rapids: "The policies of the president are a continuation of what we've seen over the last four years." Volunteers for both candidates are frantically knocking doors and treading pavements across Iowa in an effort to clinch the critical six votes it will contribute to the national electoral college of 538. While the national vote is tied, Mr Obama will win re-election if he can take Iowa, neighbouring Wisconsin and nearby Ohio, while holding states already pencilled into his column. If Mr Romney loses in Ohio, where he has consistently trailed, he must construct a patchwork of smaller states – starting with Iowa. Local residents said their televisions and radios were blaring attack advertisements around the clock, while their postboxes were stuffed full with mail-outs, such as Mr Obama's new pamphlet. Yet in a setback to the president, The Des Moines Register, a powerful regional newspaper, complained yesterday that he had insisted on being interviewed "off the record", keeping his remarks secret. "The answer to one of the most important questions the Register ever can ask a politician – "Why should you be our president?" – deserves to be shared with voters," its editors wrote. Facing claims from aides to Mr Romney, who gave a full interview, that the decision "betrayed the president's lack of confidence about his failed record and lack of a vision", Mr Obama relented. The transcript showed he pledged to overhaul US immigration laws, having failed to do so in his first term as promised. He predicted Republican leaders would co-operate having "alienated the fastest-growing demographic group", Latinos, with extreme statements during the campaign. Mr Obama also reiterated his goal to strike a "grand bargain" to reduce the $1.2 trillion budget deficit via $2.50 in spending cuts for every extra dollar in tax revenue. Republicans say taxes must not rise. Supporters in Davenport said middle America backed Mr Obama's plan. "People here are worried about how to make it to the next day, how to fill their cars," said Rodney Maiden, a 40-year-old mature student. "Obama has walked in those shoes – and he hasn't forgotten. Romney has never struggled". In a feisty speech, Mr Obama claimed Mr Romney would "turn back the clock 50 years for immigrants, gays and women" and repeatedly said the Republican had shown himself to be untrustworthy. He attacked Mr Romney for claiming to be a "car guy" after opposing the government bail-out of the US auto industry – central to the Midwestern economy – and for now saying his plan to cut income taxes by 20 per cent would not benefit top earners, after privately assuring donors that it would. Listing such symptoms of "Romnesia", he joked that the prescription was ObamaCare, his health system reform. "We can cure you, Iowa!", he said. "We can cure folks of this malady, this disease." In the crowd, Mercedes Rosing, who cares for her disabled husband full-time, said she feared Mr Romney's plan to scrap ObamaCare. "We struggle with insurance costs," she said. "We need help". Mrs Rosing, 55, said times were so hard that Mr Obama's support was not guaranteed. "I thought Romney might not be so bad, that he was a moderate," she said. "But he's shifted. I'm worried what he would do".