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, Obama had a four percentage-point edge of 45 percent to 41 percent. This marks the second time this year the president has had a lead outside the poll’s margin of sampling error.

Obama’s advantage comes largely from increased support among independents, who now pick him over Romney by 11 percentage points. Some 30 percent of independents are undecided. Last month, Obama had a four-point edge among independents, while Romney had the advantage from April through early June.

There was also an uptick in support for Obama among women, blacks and Democrats.

Four voters in 10 say they are “extremely” interested in the race. Among just those voters, the candidates are tied at 48 percent each.

Click for full results from the poll.

The Obama campaign has spent heavily on advertising attacking Romney’s time at Bain Capital and his tax returns. And it appears to be working. Romney’s favorable rating dropped six percentage points since last month and now sits at 46 percent, down from 52 percent in mid-July. At the same time his unfavorable rating went up five points. Romney’s favorable rating has held steady among his party faithful, but it’s down eight percentage points among independents and seven points among Democrats.

Overall 54 percent of voters have a positive view of Obama, matching his highest favorable rating in more than a year. Last month, it was 52 percent. Obama’s current rating is nearly as high as four years ago, when 59 percent viewed him positively.

While Democrats typically hold a slight edge over Republicans nationally in party identification, this attitude shifts based on events and changing sentiment. These days, voters seem to be even more likely to consider themselves Democrats than Republicans. There has been a five percentage-point Democratic advantage, on average, in Fox News polls this year. In this poll, the Democratic edge is nine points. That may or may not be on the high side, although it is similar to other recent national polls conducted by NBC News and the Wall Street Journal, which puts Democrats up 11 percentage points and the Pew Research Center, with Democrats up by 13 percent.

“The events of the past two weeks appear to have energized Democratic voters a bit," says Republican pollster Daron Shaw, who conducts the Fox News poll with Democratic pollster Chris Anderson. “But perhaps more critically, Romney’s support among independents has declined. The Obama campaign has -- at least in the short-term -- succeeded in raising questions about Romney’s fitness to govern and in making this less of a referendum and more of a choice election."

Most Obama supporters (83 percent) and Romney supporters (87 percent) say they are “certain” to vote for their candidate. Nearly one in four independent voters says they could change their mind before voting (24 percent).

Setting aside how they plan to cast their ballot, the poll asks voters about their comfort level with each candidate being the country’s leader. Eight percent would be “extremely” comfortable with Romney as president. Two-and-a-half times as many -- 21 percent -- feel that way about a second Obama term.

Some 26 percent would be “extremely” or “very” comfortable with Romney as president, 33 percent “somewhat” comfortable and 38 percent “not at all.”

For Obama, 41 percent of voters would be at least very comfortable with him serving another four years, while 22 percent would be “somewhat” comfortable and 37 percent would not be comfortable with another term.

Independents are twice as likely to say they are comfortable with Obama (33 percent) than with Romney (16 percent) as president.

The top reasons voters give for being uncomfortable with Romney include his positions on the issues, that he’s “phony,” he’s “out of touch,” he’s a Republican and he’s “for the rich.” For Obama, the discomfort comes from his performance as president, unemployment/no economic recovery, his positions on the issues, “everything,” and his health care plan.

Fully 76 percent of Democrats think Obama’s positions on the issues are “about right.”

Likewise the GOP challenger has convinced most Republicans of his ideology. Some 73 percent of Republicans say he’s “about right” on the issues, up from 57 percent last year (September 2011).

Less than half of independents think either candidate is “about right” on the issues.

Meanwhile, Obama is trusted more than Romney on foreign policy (13 points), helping people achieve the American dream (+8 points), national security (+ 8 points), health care (+ 7 points) and stopping Iran from getting nuclear weapons (+4 points).

More voters trust Romney to do a better job on reducing the deficit (+ 8 points) and improving the economy (+3 points) -- the most important issue to voters this election. Two months ago, Romney had a seven-percentage point edge on handling the economy (June 3-5).

A 56-percent majority says the economy will be “extremely important” to their vote for president. That’s far more than say the same of health care (45 percent), national security (44 percent), taxes (39 percent), foreign policy (30 percent) and immigration (25 percent).

If Obama were re-elected, 48 percent of voters say they would feel the “country’s improving” and they would “look forward” to another four years, while almost as many -- 42 percent -- say they would feel the country is “going down the drain” and would “dread” a second term.

That’s similar to the president’s overall job rating: 49 percent of voters approve and 46 percent disapprove. In July, 47 percent approved and 49 percent disapproved.

The president hasn’t hit 50 percent approval since May 2011, when after the raid that killed Usama bin Laden some 55 percent approved and 41 percent disapproved.

The Fox News poll is based on landline and cell phone interviews from August 5 to August 7 among 930 randomly-chosen registered voters nationwide. The poll is conducted under the joint direction of Anderson Robbins Research (D) and Shaw & Company Research (R). For the total sample, it has a margin of sampling error of plus or minus three percentage points.