The biggest hurdle for Republican Mitt Romney to overcome in his six-plus years’ pursuit of the White House has been authenticity.

On a range of issues – from abortion, health care, climate change, and coal to the minimum wage, campaign finance, and bank bailouts, to name a few – Romney has shifted positions and even been diametrically opposed to views he had held previously.

It’s something that’s haunted him dating back to 1994 – in his first venture into politics – when he ran for the Senate against the late Ted Kennedy. “Mitt Romney isn't pro-choice; he's not anti-choice; he's multiple choice,” Kennedy said of Romney’s stance on abortion in a memorable line from a Kennedy-Romney debate.

The damning line set in motion a powerful narrative that would be used against Romney for the next 18 years.

Now, with just two weeks to go until Election Day and with Romney’s path to power in sight, likely the final Romney re-positioning of this campaign took place Monday night at the third and final presidential debate on foreign policy.

The Republican nominee's moderated tone and deviation from prior positions – on timelines in Afghanistan, support for the war in Iraq, the president’s pursuit of sanctions and diplomacy with Iran, whether Egypt’s longtime leader Hosni Mubarak should have stayed in power, and whether Palestinians and Israelis can accomplish peace – are once again raising questions about Romney’s core convictions and how exactly he would intend to conduct U.S. foreign policy if elected president in 13 days.

To be fair, there have been shifts by President Barack Obama, too – from his staunch opposition to health-care mandates as a candidate to then endorsing them as president and trade policy from the 2008 primary to general election. On foreign policy, he was hotly critical of President George W. Bush’s establishment of a prison at Guantanamo Bay, Cuba, pledging to close it within a year. He tried to close it, but ran into the political and legal complications.

But it’s particularly striking that Romney -- who is 65 years old and wants to assume the role of “leader of the free world” – would at this late stage be shifting his worldview.

“Gov. Romney appeared to leave a lot of his positions behind,” former Ambassador Nick Burns, who has worked for both Republicans and Democrats, said Tuesday morning on CNN. “And it does leave you with the question – what is his worldview, what does he really believe, what would he DO on these big national security issues, such as Afghanistan or even Iran, where previously he had been very critical? Last night, [he] largely agreed with the president, so I think he’s leaving the impression that he’s not quite sure what he’d do or that he’s not being as specific as he might be.”

On Afghanistan, Romney was against a timeline for withdrawal before he was for it.

Here’s what Romney said Monday night:

“Well, we're going to be finished by 2014, and when I'm president, we'll make sure we bring our troops out by the end of 2014. … We've seen progress over the past several years. The surge has been successful and the training program is proceeding apace. There are now a large number of Afghan Security Forces, 350,000 that are ready to step in to provide security and we're going to be able to make that transition by the end of 2014. So our troops will come home at that point.”

But previously, he called the president’s timeline a “politically timed retreat,” “misguided,” “naïve,” and “makes absolutely no sense.” Here he was July in his speech to the VFW:

“I have been critical of the President’s decision to withdraw the surge troops during the fighting season, against the advice of the commanders on the ground. President Obama would have you believe that anyone who disagrees with his decisions is arguing for endless war. But the route to more war – and to potential attacks here at home – is a politically timed retreat. As president, my goal in Afghanistan will be to complete a successful transition to Afghan security forces by the end of 2014. I will evaluate conditions on the ground and solicit the best advice of our military commanders. And I will affirm that my duty is not to my political prospects, but to the security of the nation.”

Here he was Feb. 1:

“The president’s mistakes, some of them are calculated on a philosophy that’s hard to understand and, sometimes, you scratch you head and say: How can he be so misguided and so naive? Today, his secretary of defense unleashed such a policy. The secretary of defense said that on a day certain, the middle of 2013, we’re going to pull out our combat troops from Afghanistan. He announced that. He announced that. So the Taliban hears it, the Pakistanis hear it, the Afghan leaders hear it. Why in the world do you go to the people that you’re fighting with and tell them the date you’re pulling out your troops? It makes absolutely no sense. His naiveté is putting in jeopardy the mission of the United States of America and our commitments to freedom. He is wrong. We need new leadership in Washington.”

March 2010:

“I would not have announced the date we're going to start pulling people out. I think that makes it more difficult at the time you're just adding troops.”

April 2010:

“If I'm Karzai, I say holy cow before the job is done these guys are going to leave. What does that mean about my life and livelihood?”

On Iraq, Romney Monday night said:

“We don't want another Iraq, we don't want another Afghanistan. That's not the right course for us.”

Yet during another debate in Boca Raton four years ago (January 2008), Romney called the war in Iraq the “right decision.”

TIM RUSSERT: Governor Romney, was the war in Iraq a good idea, worth the cost in blood and treasure we have spent? ROMNEY: It was the right decision to go into Iraq. I supported it at the time. I support it now.

During this campaign, he shifted his position slightly, saying instead that it was “appropriate at the time.” He said on FOX News Sunday, Dec. 18, 2011:

"Going back and trying to say, given what we know now, what would we have done, would we have invaded or not, at the time, we didn't have the knowledge that we have now. … we took action which was appropriate at the time."

He also said during that same interview, he said that Obama had “pulled our troops out in a precipitous way, and we should have left 10, 20, 30,000 personnel there to help transition to the Iraqis' own military capabilities."

Asked then if he, as president, would send them back in, Romney sidestepped:

“I think the decision to send U.S. troops into a combat setting is a very high threshold decision. This is not something you do easily. You don't - you don't send our troops around the world every time there's something that goes off… in an untoward way. … I'm not going to say where I would send troops and not send troops. We send troops where there's a substantial U.S. interest involved. And I have a very high threshold as to a decision where we send our troops.”

But, according to his foreign policy white paper on his campaign website, he would have wanted 14,000-18,000 troops in Iraq:

"Reports indicate that President Obama is seeking to keep 3,000 troops in the country after 2011, a number far below the reported 14,000 to 18,000 our commanders in the field have recommended as the minimum necessary to carry out our mission. In light of these developments, it is impossible to forecast what conditions in Iraq will confront the next American president in January 2013. Mitt Romney will enter office seeking to use the broad array of our foreign-policy tools - diplomatic, economic, and military - to establish a lasting relationship with Iraq and guarantee that Baghdad remains a solid partner in a volatile and strategically vital region."

Obama, too, wanted to leave some troops in Iraq, but he ultimately couldn't get agreement with the Iraqi government to do so on the Status of Forces Agreement, which Romney attacked him for during the debate.

On Iran, Romney Monday night called for tightening sanctions, but acknowledged “crippling sanctions” are in place and working:

“…[C]rippling sanctions are something I called for five years ago, when I was in Israel, speaking at the Herzliya Conference. I laid out seven steps, crippling sanctions were number one. And they do work. You're seeing it right now in the economy. It's absolutely the right thing to do, to have crippling sanctions. I would have put them in place earlier. But it's good that we have them. Number two, something I would add today is I would tighten those sanctions.

But at a February CNN debate, during the GOP primary, Romney said Obama did not put in place “crippling sanctions.”

“This president -- this president should have put in place crippling sanctions against Iran, he did not. He decided to give Russia -- he decided to give Russia their No. 1 foreign policy objective, removal of our missile defense sites from Eastern Europe and got nothing in return. He could have gotten crippling sanctions against Iran. He did not.”

On Meet the Press last month, he said Obama’s policy of engagement “has not worked,” said U.S. “should pursue kind of crippling sanctions” he’s spoken about.

“President Obama had a policy of engagement with Ahmadinejad. That policy has not worked and we're closer to a nuclear weapon as a result of that. I will have a very different approach with regards to Iran. And it's an approach which, by the way, the president's finally getting closer to. It begins with crippling sanctions. That should have been put in place long ago. … “Well, at the time President Bush was president, Iran was years away from a nuclear weapon. And he pursued diplomacy, as I can think we should continue to pursue diplomatic channels. We should pursue as well the kind of crippling sanctions that I've spoken about when I gave a speech at the Herzliya Conference five years ago.”

Even that appearance on Meet the Press, in which he said he think “we should continue to pursue diplomatic channels,” was a rhetorical shift.

He stressed diplomacy and “peace” Monday night:

“It’s also essential for us to understand what our mission is in Iran, and that is to dissuade Iran from having a nuclear weapon through peaceful and diplomatic means.”

But here he was at AIPAC March 6, saber-rattling:

“Hope is not a foreign policy. The only thing respected by thugs and tyrants is our resolve, backed by our power and our readiness to use it.”

It’s instructive to read more of Romney’s AIPAC speech to fully grasp the tonal shift in Monday night’s debate.

“In recent days and weeks, we’ve heard a lot of words from the administration. Its clear message has been to warn Israel to consider the costs of military action against Iran. I do not believe that we should be issuing public warnings that create distance between the United States and Israel. Israel does not need public lectures about how to weigh decisions of war and peace. It needs our support.”

And:

“I will bring the current policy of procrastination toward Iran to an end. I will not delay in imposing further crippling sanctions, and I will not hesitate to fully implement the ones we currently have. I will make sure Iran knows of the very real peril that awaits if it becomes nuclear. … As President, I will be ready to engage in diplomacy. But I will be just as ready to engage our military might.”

On negotiations:

“I have studied the writings and speeches of the jihadists. They argue for a one-state solution—one all-dominating radical Islamist state, that is. Their objective is not freedom, not prosperity, not a Palestinian state, but the destruction of Israel. And negotiating and placating such jihadists will never, ever yield peace in the Middle East. I recognize in the ayatollahs of Iran the zealot refrain of dominion.” … “Iran has long engaged in terrorism around the world, most recently in Georgia and in Thailand. In Washington, DC, Iran plotted to assassinate the Saudi ambassador by bombing a Georgetown restaurant. Iran has deployed Hezbollah and Hamas and armed the insurgents of Iraq and Afghanistan, killing our sons and daughters. They war against America. Yet, the current administration has promoted a policy of engagement with Iran.”

And on sanctions:

“This President not only dawdled in imposing crippling sanctions, he has opposed them.”

On Mubarak, Monday night, Romney said he approved of how the president handled the ouster of longtime Egyptian President Hosni Mubarak:

MR. SCHIEFFER: Governor Romney, I want to hear your response to that, but I would just ask you, would you have stuck with Mubarak? MR. ROMNEY: No, I believe, as the president indicated and said at the time, that I supported his — his action there.

But here was Romney on July 27 critical of President Obama’s handling of Mubarak, telling an Israeli newspaper that Obama could have persuaded Mubarak to become more democratic – not calling for his ouster:

“President Bush urged Hosni Mubarak to move toward a more democratic posture, but President Obama abandoned the freedom agenda and we are seeing today a whirlwind of tumult in the Middle East in part because these nations did not embrace the reforms that could have changed the course of their history, in a more peaceful manner.”

On the prospect of Israeli-Palestinian peace, Monday night Romney criticized the president for not doing more to accomplish it:

“...are Israel and the Palestinians closer to — to reaching a peace agreement? No, they haven’t had talks in two years. We have not seen the progress we need to have, and I’m convinced that with strong leadership and an effort to build a strategy based upon helping these nations reject extremism, we can see the kind of peace and prosperity the world demands.”

But Romney’s public and private comments have diverged on this subject.

Publicly, he told the Israeli newspaper Haaretz:

“I believe in a two-state solution which suggests there will be two states, including a Jewish state.”

But privately, during that fundraiser in which he called 47 percent of Americans “victims,” he dismissed the idea of a two-state solution and said it would “remain an unsolved problem”:

“Palestinians have no interest whatsoever in establishing peace and that the pathway to peace is almost unthinkable to accomplish. … These are problems that are very hard to solve. And I look at the Palestinians not wanting to see peace anyway, for political purposes -- committed to the destruction and elimination of Israel. I just say there is no way, and so, what you do is you move things along the best way you can and hope for some degree of stability, but you recognize this is going to remain an unsolved problem.”

During his speech at AIPAC, instead of maintaining neutrality with regard to negotiations, he said:

“The current administration has distanced itself from Israel and visibly warmed to the Palestinian cause. It has emboldened the Palestinians. They are convinced that they can do better at the UN – and better with America – than they can at the bargaining table with Israel. As President, I will treat our allies and friends like friends and allies.”

During his trip in Israel, at another fundraiser, he also implied that it was Palestinians’ “culture” that was to blame for lower gross-domestic product in areas controlled by the Palestinian Authority as compared to Israel.

Despite all of these shifts, Romney adviser Jim Talent, a former Missouri senator, claimed on MSNBC’s Andrea Mitchell Reports that it was Obama who was shifting -- toward Romney.

“I gotta tell you. I think the opposite is true,” he said after being asked about Romney’s changes. “I think the president is moderating his view to come closer to Mitt Romney’s view.”

Closer to the “mainstream,” Talent said.

NBC's James Rankin contributed to this report.