In 2008 Barack Obama stood before a 200,000-strong crowd in Berlin and declared that "now is the time to build new bridges across the globe" - but did he ever intend to pursue the foreign policy his liberal well-wishers expected of him?

If you are running to be the next US commander-in-chief, it pays to talk tough.

Recently, the Republican presidential nominee Mitt Romney called President Barack Obama "weak" after anti-American violence erupted in the Muslim world.

The Obama administration has endorsed many of the Bush administration's national security policies Jameel Jaffer, American Civil Liberties Union

President Obama, of course, has a killer comeback: "Al-Qaeda is on the path to defeat," he has proclaimed, "and Osama Bin Laden is dead."

After four years in office, the president hopes the image of a man unafraid to use military force might help woo American voters.

But what about those liberals around the world who cheered Obama's election - and those who awarded him the Nobel Peace Prize after just a year in office? Should they feel disappointed with the toughness of the man in the Oval Office?

Back in 2008, many hoped Obama's election would usher in a new and more peaceful era in world affairs. Guantanamo Bay would soon close. US military operations and strikes in the Muslim world would abate. The mooted American invasion of Iran would soon be off the table.

These wishes did not come true.

Obama = Bush?

For the BBC's Analysis programme, I have been speaking to key US insiders and experts who chart a clear shift in President Obama's foreign and security priorities.

Image caption President Obama was presented the Nobel Peace Prize in 2009

The tone has certainly been more mellow than the George W Bush years, and American troops are out of Iraq. But on national security in particular, there is a striking consensus among experts that Obama has embraced some of the most controversial doctrines of George W Bush's "war on terror".

"The Obama administration has endorsed many of the Bush administration's national security policies," says Jameel Jaffer, director of the American Civil Liberties Union - a leading US liberal rights group.

Mr Jaffer says this includes "policies that were regarded three or four years ago as the most extreme of the Bush administration's policies."

The most symbolic example is the prison at Guantanamo Bay, which Obama promised to close within a year during his 2008 election campaign, but which continues to detain inmates indefinitely and subject them to military trials, rather than trials in open court.

It may be unfair to blame President Obama for this - he initially tried to close Guantanamo but was ultimately blocked by Congress.

"But the administration does have the ability to fight back against those restrictions," counters Jaffer.

"The administration does have the ability to go to the American people and say these restrictions don't make any sense. That's something that the president could have said and didn't."

In fact, says Jaffer, other controversial Bush-era measures have actually increased under President Obama.

In Yemen, for example, there are at least two parallel programmes of targeted killings by remotely controlled drone aircraft - but little more is known, because these operations are covert.

'Obama different to Bush' I think Obama sees American power as a force for good. I think American presidents almost always see American power as a force for good. What sets President Obama apart is he is probably the most global of our presidents ever. I think Obama and George W Bush are substantively different. The first thing to recognise is that Bush launched two wars and Obama has ended one and is ending the second. So our overall posture in terms of the use of the military has changed dramatically. The second big change is that it's not a war on terror anymore. It's a war on individual terrorists - and there he has absolutely stepped up the drone programme. He's gone after individual al-Qaeda members fiercely. But the other side of that coin is that he no longer says wherever people operate who may support terrorists, we are at war with those countries - we're at war with terror across the world - which was really a never-ending war and one that really poisoned relations, particularly with Muslim majority countries. Prof Slaughter was director of policy planning for the US State Department from 2009 to 2011 How Obama wields America's power

The UK's Bureau of Investigative Journalism collates reported deaths under drone strikes, and estimates there have been about 500 this year in Yemen alone. It is impossible to be sure how many of these are militants and how many are civilians.

Even some of President Obama's closest allies worry about the fact that there is no judicial process before these killings. The president simply gives the order to strike, and has even targeted US passport holders in Yemen - such as the radical Muslim cleric Anwar al-Awlaki - as well as foreign nationals.

"The idea that these strikes can happen against foreign citizens, but also American citizens, without trial, is something that should give any American citizen pause," says Prof Anne-Marie Slaughter of Princeton University, who until last year worked as director of policy planning for Obama's Secretary of State Hillary Clinton.

Most strikingly of all, it is not just embittered liberals who say Obama has taken on Bush's national security policy.

"Barack Obama has, to a remarkable degree, continued George W Bush's national security policy," says Jack Goldsmith, who served as an assistant attorney general in the first GWB administration.

Goldsmith, a leading conservative lawyer and Harvard law professor who is now publishing a book on the subject, says that the courts and Congress refined the original "war on terror" policies over time.

They introduced certain safeguards and so the Obama administration grew to not only accept them - but in some cases "learned to love" them.

For example, in 2006 the US Supreme Court ruled military trials at Guantanamo to be illegal unless Congress approved standards for them - which Congress later did.

This made the policies acceptable to Obama, despite his initial pledges, says Goldmsith.

"They were, in a very real sense, the nation's policies... they had been blessed as lawful."

"This is not a pacifist president, not even a left-wing president," says Stephen Walt, professor of international affairs at Harvard's Kennedy School of Government.

"In some respects, he's been quite hawkish, maybe even slightly right of centre."

'Bad boyfriend benefit'

In some ways it is unsurprising that the Obama administration has been tough on national security - after all, until recently, Osama Bin Laden was still on the loose.

Obama's hawkish foreign policy I think in terms of style he has continued to be very different than George W Bush - more thoughtful, very few moments where he says something that's really tactless or needlessly provocative, particularly in dealing with international audiences. But if you look at the actual policies, particularly in foreign policy, the differences between the Obama administration and Bush's second term - not the first term, but the second term - are not that great. He has adopted a rather hawkish foreign policy. He escalated the war in Afghanistan - which is something he did not need to do. He made a brief attempt to reach out to Iran, but it was rather half-hearted and it was very short-lived, and he has reverted to what was essentially the Bush administration's policy towards Iran. Finally, President Obama has been a very enthusiastic user of drones and special forces - not just in Afghanistan and Pakistan, but in a number of other places, most notably Yemen. He has not been bashful about using American military force - in smaller doses than President Bush, no big invasions, no big occupations - but he has not been shy about using the pointed end of American power to go after perceived bad guys with all of the potential negative consequences. Stephen Walt is professor of international affairs at Harvard University. Is Barack Obama a Tory?

But what about in wider foreign policy? Scholars say that here too there has been a shift away from the early tone of "engagement" towards a more assertive stance.

"When President Obama took office, the first job was to reintroduce America to the world," says Prof Anne-Marie Slaughter.

"President Obama had this vision of forging a new relationship with the Muslim world, working through international institutions rather than against them. The United States working to solve global problems - rather than to wage war and set an agenda that other nations were expected to follow."

The problem with this doctrine, say analysts, was that it relied on the countries Obama "engaged" with - such as Iran or China - to follow his lead.

Iran, it was hoped, would come to the negotiating table and abandon its nuclear programme. China would sign up to limiting its greenhouse gas emissions.

But Chinese officials clashed with Obama at the Copenhagen climate summit. Iran was unreceptive to Obama's peaceful approach - until last week when President Mahmoud Ahmadinejad told reporters that Iran is ready for talks with the US.

"The administration thought it would collect what I call the "bad boyfriend benefit"," says Daniel Drezner, professor of international politics at Tufts University.

In other words, he says, other countries would be so glad that George W Bush - a "bad boyfriend" who led the invasion of Iraq - was no longer in office that they would be more than willing to engage with Barack Obama's White House.

"That didn't happen," says Drezner. Instead, he says, the Obama administration has ended up taking assertive actions and even threatening force to make sure other countries followed international norms.

"You can argue that's partly what they did with China with respect to their policies in 2008 and 2009. That's what certainly they've done to deal with al-Qaeda, and that's what they did with Muammar Gaddafi," Drezner says.

"I do think that there was a point in the Obama administration at which it was recognised that engagement was not an end in itself," concedes Anne-Marie Slaughter.

"I do think there was a learning curve," she says. "I think there was a recognition that engagement is a tool and if it doesn't work, then you have to hold firm - you have to confront."

But she says liberals would be wrong to think Obama had ever ruled out the use of force. If you listen carefully to his early speeches, that option was always on the table.

"We will not eradicate violent conflict in our lifetimes," he said in his 2009 Nobel Prize acceptance lecture.

"There will be times when nations - acting individually or in concert - will find the use of force not only necessary but morally justified."

So perhaps it was overseas and American liberals watching Obama's election - rather than Obama himself - who imagined a more peaceful role for American foreign policy than was ever realistically possible.

James Fallows, national correspondent at The Atlantic magazine and a veteran Washington observer, tells me that Obama's tough talk on foreign affairs now reminds him of Bill Clinton - not as president but during his election campaign, when he was still governor of Arkansas.

Back in 1992, a man with obvious and severe learning difficulties, Ricky Ray Rector, was set to be executed. Clinton's liberal supporters were appalled - but he signed the death papers anyway.

"That is the reality of democratic life in a huge, sprawling system like that of the United States," says Fallows.

So what about the hopes invested in the president by the Nobel Peace Prize?

"It could have been a marker of the naivety of the world's expectations of this president and his country."

You can also listen to the full report via the Radio 4 website or Analysis download.