Mitt Romney has had a tough couple of weeks on the campaign trail -- and it shows in the latest Fox News poll. After a barrage of campaign ads, negative news coverage of his overseas trip and ongoing talk about his tax returns, Romney’s favorable rating and standing in the trial ballot have declined. As a result, President Obama has opened his biggest lead since Romney became the presumptive Republican nominee. The president would take 49 percent of the vote compared to Romney's 40 percent in a head-to-head matchup if the election were held today, the poll found. Last month,...