WASHINGTON -- Wrapping up a stumble-marred overseas trip, Mitt Romney pivoted quickly into a three-month stretch to the election on Tuesday with a new feel-good television ad. Aides simultaneously stoked speculation about his vice-presidential pick.

The economy was Romney's primary text abroad as well as at home. "We could probably learn something from what's happening right here," the former Massachusetts governor said of Polish policies shortly before boarding his chartered jet for the flight back to the U.S.

Advisers accompanying him said he would resume direct criticism of President Barack Obama's record soon enough, after observing a mini-moratorium while on foreign soil. Yet a new television commercial suggested another immediate priority was to close a likeability gap in the polls.

Shorn of any criticism of Obama, the ad appears designed to introduce Romney to voters in battleground states who know little or nothing about his personal background except what they've seen and heard in unflattering commercials aired by Democrats.

In the ad, Romney speaks of his years in private business, in government and as the head of the Olympic Games in Salt Lake City a decade ago and says, "I want to use those experiences to help Americans have a better future."

In the final hours of his trip, in Warsaw, the Republican extolled the Polish economy as a model for the rest of the world in an era of slow growth or worse, and he simultaneously sought to limit the political fallout caused by comments he made earlier on a stop in Israel.

"The world should pay close attention to the transformation of the Polish economy" since the end of communist rule more than two decades ago, he said in a speech in the Polish capital city. "A march toward economic liberty and smaller government has meant a march toward higher living standards, a strong military that defends liberty at home and abroad and an important and growing role on the international stage.

'Rather than heeding the false promise of a government-dominated economy, Poland sought to stimulate innovation, attract investment, expand trade and live within its means," he added.

It was thinly veiled criticism -- one of several instances on the trip -- of the policies Obama has pursued while in office, and Romney was slightly less veiled in a Fox News interview. He did not mention that joblessness in Poland is over 12 per cent, roughly half again as much as in the United States.

With just under 100 days until the election, the presidential race remains a tight one, likely to be decided by a relative sliver of undecided voters who live in eight or so states that remain competitive. Romney heads to one of them on Thursday, when he resumes traditional campaigning with an appearance in the Denver area.

His time to pick a running mate is dwindling, with the Republican National Convention set to open on Aug. 27 in Tampa, Fla. His campaign unveiled an app for smartphones that officials said would "serve as the campaign's first official distribution channel" for the news of his choice. Separately, Republican officials noted an announcement could come any day.

As for one of the controversies on his trip, Romney said in the interview with Fox before leaving Europe that he hadn't been speaking about "the Palestinian culture or the decisions made in their economy" in his remarks earlier in the week that prompted one Palestinian official to question whether his views were racist.

At a fundraiser with Jewish donors in Jerusalem, Romney had said their culture was part of what had allowed them to be more economically successful than the nearby Palestinians. He made no mention of the fact that Israel has controlled the West Bank, Gaza Strip and East Jerusalem since capturing them in the 1967 war, a presence that the World Bank and International Monetary Fund both say limits the economy's potential for growth there.

In Poland as on other stops, Romney ignored shouted questions from reporters about his comments on Israel and the Palestinians. Asked why the former Massachusetts candidate had responded to just three questions from American reporters during the trip, travelling press secretary Rick Gorka said, "Shove it."

The aide later called some journalists to apologize.

Aides later said that despite any mistakes made during the trip, there was little evidence they would materially affect the campaign.

"I don't think that will go down in history as very important," said Stuart Stevens of possible missteps.

Nor is it likely that Romney will suffer politically from any clash with the news media, nor suffer damage among Jewish voters for comparing Israelis favourably with the Palestinians.

While Obama's aides and campaign staff missed no chance to pan Romney's performance, it remains unclear whether the former Massachusetts governor achieved his goal of demonstrating to the public an ability to stride confidently across the world stage.

Of evident concern is polling indicating that while the voting public generally believes Romney has better economic policies than Obama, it views the president in more favourable terms personally.

In an NBC News/Wall Street Journal poll completed on July 22, some 49 per cent of registered voters said they had positive feelings toward Obama while 35 per cent said the same about Romney.

In the same survey, 43 per cent of registered voters said Romney would be better at dealing with the economy, while 37 per cent said Obama would.

The new Republican ad was a joint venture of the Romney campaign and the Republican National Committee

"We believe in our future, we believe in ourselves, we believe the greatest days in America are ahead," Romney says as American flags flutter.

With the race near deadlock for months, ad spending was soaring in battleground states and non-existent in others.

The Obama campaign also unveiled a new commercial during the day, part of what detailed advertising records show is a heavy investment in the range of $30 million during August.

In the Fox interview, Romney suggested the news media were to blame for the culture controversy, saying some will 'try to find anything else to divert from the fact that these last four years have been tough years for our country.'

There were other uneven moments on what Romney and his aides had planned as an illustration of his ability to handle the world stage. In London, he drew a tart response from Prime Minister David Cameron after wondering aloud whether the British had adequately prepared for the Olympic Games now under way.

And in a speech in Jerusalem he declared that the city is the capital of Israel, even though the U.S. has its embassy in Tel Aviv and maintains a policy that the city's designation is a matter for negotiations between the Jewish state and Palestinians.

Not surprisingly, he got nothing but criticism from the president's surrogates.

Robert Gibbs, a senior campaign adviser, called the trip "an embarrassing disaster" for Romney. "He both offended our closest ally and triggered a troubling reaction in the most sensitive region of the world. He certainly didn't prove to anyone that he passed the commander-in-chief test," Gibbs said.