WASHINGTON (AP)  President George W. Bush agreed to seek "a general time horizon" for deeper reductions in American combat troops in Iraq, a dramatic policy shift that complicates an issue on which presidential candidates Barack Obama and John McCain have staked opposite positions. Bush's announcement came as Obama geared up for a Europe and Mideast trip aimed at helping him bolster his foreign policy and national security credentials, an area in which Republicans say his experience is inadequate for the White House. The Democrat, who is seeking to become the first black U.S. president, has spent much of the week outlining his foreign policy views, even as the faltering U.S. economy has eclipsed Iraq as the top campaign issue in the November election. IRAQ PLAN: Iraq, U.S. agree on 'general time horizon' Obama, whose schedule includes visits Iraq and Afghanistan, has pledged to withdraw combat troops within 16 months if he is elected, and argues that McCain offers nothing more than an extension of Bush's unpopular policies. He has maintained that McCain would do little more than continue a war that has diverted necessary U.S. forces from the conflict in Afghanistan where Taliban and al-Qaeda militants are regrouping, posing a renewed risk to Americans. The presumptive Republican nominee, a former Navy pilot and Vietnam prisoner of war, has trumpeted his foreign policy credentials while trying to focus his campaign on the country's economic struggles. McCain's efforts to portray himself as an economic leader took a hit earlier this month when a top policy adviser, former senator Phil Gramm, said the United States had become a "nation of whiners" who constantly complain about the economy. On Friday, Gramm resigned from his role as co-chair of the McCain campaign, saying in a statement that he wanted to "end this distraction." Earlier in the day, in an appearance before General Motors workers in Michigan, McCain once again sought to counter the impression that he was not as strong as Obama on the economy. He promised the auto workers that he would help make the company's long-range electric car a success as he outlined ways to help a state and industry hit hard by the economy. But foreign policy remained a key focus. The veteran Arizona senator aired a new TV ad saying that while Obama has not been to Iraq for years, and voted against war funding to win the Democratic nomination, he is now "changing to help himself become president." McCain, it says, has always supported the Iraq strategy "that's working" — a reference to the troop buildup credited for sharply reducing violence in the country. But Bush's announcement after repeated pressure on the issue from Iraqi leaders appears to put him at odds with McCain, and could make his own administration a tougher target for Obama's criticisms. The plan comes as Bush and Iraq's prime minister have talked about the timing of the force drawdown as part of discussions over a broader security agrement to keep U.S. forces in the country after the expiration of a U.N. mandate on Dec. 31. Iraqi officials, buoyed by recent security gains, have proposed that U.S. forces fully withdraw five years after the Iraqis take the lead on security across the country. That condition, however, could take years to materialize. The accord would include "a general time horizon" for meeting goals like "the resumption of Iraqi security control in their cities and provinces and the further reduction of U.S. combat forces from Iraq." That could sap some of the strength from Obama's push to appear as the candidate most ready to bring an end to a conflict that's in its sixth year. Obama's trip was at least partly aimed at highlighting that strength. It affords the first-term Illinois senator — who currently leads McCain in many polls but is, at best tied on those relating to foreign policy — a chance to promote his plans to mend rifts with allies weary of the Bush administration and end the Iraq war. Campaign officials have announced stops in Jordan, Israel, Germany, France and England. Aides have not said whether the Iraq and Afghanistan trips will be part of the same trip. The visits could also factor in his favor in further invigorating supporters and winning over others like independents and swing voters. An Associated Press-Yahoo News poll showed that Obama's supporters are much more energized by the election than McCain's are. It showed that 38% of Obama's supporters say the election is exciting compared with 9% of McCain's. The passion and interest shown by blocs of voters are important because they affect who will be motivated to vote. In addition, 65% of Obama's backers say they are hopeful about the campaign, double McCain's, and the Democrat's supporters are three times likelier to express pride. But not all Democrats are equally intrigued with Obama. The poll showed 31% of those supporting Obama are Democrats who had preferred former rival Hillary Rodham Clinton during the party's primary battle. Just 12% of former Clinton supporters say they are excited about the campaign, one-third of the excitement level among Obama's longer-term backers. Independents, whom both McCain and Obama are avidly pursuing, show little enthusiasm about the race. Only 21% find the election interesting — down from 31% in November — and just 7% say it is exciting. Substantial numbers say they feel frustrated, helpless and even bored. The AP-Yahoo News poll, conducted by Knowledge Networks, has measured the political sentiments of the same 2,000 adults since November. Friday's poll was conducted from June 13-23 among 1,759 adults and has an overall margin of sampling error of plus or minus 2.3 percentage points. Copyright 2008 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed. 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. Use the "Report Abuse" button to make a difference. 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. Use the "Report Abuse" button to make a difference. Read more