The Gallup organization first started asking Americans how they approved of the job the president was doing in the 1940s. See how each president since then has fared in the approval poll, look at some news events that influenced public opinion and compare how approval ratings evolved for each president.

PRESIDENTIAL APPROVAL TRACKER PRESIDENTIAL APPROVAL TRACKER The Gallup organization first started asking Americans how they approved of the job the president was doing in the 1940s. See how each president since then has fared in the approval poll, look at some news events that influenced public opinion and compare how approval ratings evolved for each president. Although the Gallup organization started asking Americans their opinions on presidential job performance during Franklin Roosevelt's term, Harry Truman's presidency was the first that the question was asked from the start of the term. Even then, Gallup asked the question infrequently. Now, Gallup's public opinion polls come out frequently. Although each poll is only a snapshot in time, over the course of history, the polls tell an interesting story about each presidency and American attitudes. — By William Couch, Michelle Price and Joshua Hatch, USA TODAY WASHINGTON  A president's standing after his first six months in office doesn't forecast whether he'll have a successful four-year term, but it does signal how much political juice he'll have for his second six months in office. That's the lesson of history. ISSUES: Faith in Obama's economic strategy declines Barack Obama, who completed six months in office Monday, has a 55% approval rating in the USA TODAY/Gallup Poll, putting him 10th among the dozen presidents who have served since World War II at this point in their tenures. That's not as bad for Obama as it may sound: The six-month mark hasn't proved to be a particularly good indicator of how a president ultimately will fare. Two-thirds of Americans approved of the jobs Jimmy Carter and George H.W. Bush were doing at six months, but both would lose their bids for re-election. And though the younger Bush and Bill Clinton had significantly lower ratings at 180 days — Clinton had sunk to 41% approval — both won second terms. Even so, a president's standing at the moment is more than a matter of vanity. It affects his ability to hold the members of his own party and persuade those on the other side to support him, at least on the occasional issue. "Approval ratings are absolutely critical for a president achieving his agenda," says Republican pollster Whit Ayres. For Obama, the timing of his slide in ratings is particularly unhelpful: He's intensified his push to pass health care bills in the House and Senate before Congress leaves on its August recess. He'll press his case at a news conference at 8 p.m. Wednesday. His overall approval rating has dropped 9 percentage points since his inauguration in January, and his disapproval rate has jumped 16 points, to 41%. Trouble at home More people disapprove than approve of Obama on four domestic issues: the economy, taxes, health care and the federal budget deficit. He scores majority approval on handling Iraq, Afghanistan and foreign affairs. The biggest drop has been on his handling of the economy, down 12 points since February; his disapproval is up 19 points. The most erosion has come not from Republicans or independents but among his own Democrats. Support from conservative and moderate Democrats is down by 18 points. Another group in the party's political base — those earning $20,000 to $50,000 a year — had a drop of 15 percentage points, to 47%. That could reflect one reason why moderate Democratic senators and the fiscally conservative Blue Dog Democrats in the House are demanding more cost controls in the health care plan before they'll sign on. "It's important if a president is trying to accomplish some big stuff legislatively," H.W. Brands, a professor at the University of Texas-Austin, says of the approval rating. He was one of several presidential historians who sat down with Obama at a private White House dinner this month. "Members of Congress are somewhat reluctant to tangle with a president who seems to have the backing of the American people." At 55% overall, Obama's approval rating is a tick below that of George W. Bush at six months. It is well above Clinton and Gerald Ford, who was hammered for his pardon of Richard Nixon. At the top of the list is Harry Truman at 82% — buoyed by the end of World War II — followed by Lyndon Johnson, John Kennedy and Dwight Eisenhower. The fact that presidents from the 1950s and 1960s scored better than more recent ones could mean the public's assessments are getting tougher. "Mid-20th-century presidents had higher political capital and more stable political capital than presidents of the last 20 years," says Steven Schier, a political scientist who is studying presidential job approval since modern polling began in the 1930s. He wrote Panorama of a Presidency: How George W. Bush Acquired and Spent His Political Capital. Schier theorizes that the difference in ratings is due to the accelerating speed with which information is disseminated, the declining number of Americans firmly tied to a political party and a growing desire to see quick results. "There's less patience with presidents than there used to be," he says. What's popularity for? Savvy presidents understand that pursuing big policies will cost them popularity, Brands says. "Presidents have to decide what their popularity is for," he says. "Lyndon Johnson probably understood best that political popularity is a wasting asset. You had to use it when you had it." Johnson was inaugurated after Kennedy's assassination in 1963 and then crushed Republican Barry Goldwater in the 1964 presidential race. LBJ used his high approval ratings — they didn't fall below 60% for more than two years after his inauguration — and big majorities in the House and Senate to enact his Great Society programs. Amid growing opposition to the Vietnam War, Johnson's standing fell so low that he decided not to seek another term. Ronald Reagan may provide a closer parallel to Obama. Both took office as the nation's economy was in perilous times. Reagan was at 60% at six months, but his standing slipped below 50% by the end of his first year in office as the jobless rate swelled. It would take two years and economic recovery before a majority of Americans would approve of his presidency again. Guidelines: You share in the USA TODAY community, so please keep your comments smart and civil. Don't attack other readers personally, and keep your language decent. 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