(CNN) When protests erupted in Iran in 2009, then-President Barack Obama reacted cautiously, concerned that a forceful intervention could make America -- reviled as the "Great Satan" by Iranian revolutionaries -- a rallying cause for the clerical regime.

Eight years on, with demonstrations and violence breaking out again in Iranian cities, the US position is reversed, with President Donald Trump and his team almost gleefully leaping at the chance to line up alongside Iranian protesters.

In one of his first tweets of the new year, Trump was openly rooting for regime change.

"Iran is failing at every level despite the terrible deal made with them by the Obama Administration. The great Iranian people have been repressed for many years. They are hungry for food & for freedom. Along with human rights, the wealth of Iran is being looted. TIME FOR CHANGE!"

The sharp change of tack reflects the gulf in the intellectual and temperamental approach of the last two presidents and illuminates a dispute between rival schools of foreign policy thought about how the US should act and wield power in the world.

It is consistent with the hard line Trump has taken toward Iran, muscling up alongside US allies Israel and Saudi Arabia to try to check the country's regional influence while continually casting doubt on the Obama-era nuclear deal with Tehran.

Trump's position also represents a return to an elusive hope that has often characterized Washington's approach to Tehran since the revolution in 1979 -- that a political awakening will sweep the revolutionary regime away -- combined with a belief that tough US talk can be a catalyst for change.

And it is in tune with Trump's habit of repudiating the approaches of his predecessor. Republicans now argue that latest repression exposes Obama's deal to freeze and reverse Iran's nuclear program as a failure, even though its proponents insist it was always meant to deal with only the most dangerous aspect of the toxic US-Iran relationship: the concern over the possibility the country could develop nuclear weapons.

Still, four days into the Iranian protests, there is no sign yet that Trump will do much more than cheer the protests from the sidelines. There is also no indication that the demonstrators would actually welcome a US role, raising doubts over the influence Washington actually has in shaping an uprising being driven by internal political dynamics in Iran, especially economic discontent.

The death toll in the protests had climbed to 12 by Monday, according to reports in the state-run Iran newspaper, which cited the Islamic Republic of Iran Broadcasting network, and in the Islamic Students News Agency, citing the governor of Dorud, Mashallah Nemati.

Trump has been closely watching the protests build, tweeting on Friday that Iranians were showing they were "fed up with regime's corruption & its squandering of the nation's wealth to fund terrorism abroad."

The next day he tweeted out highlights of his UN General Assembly speech in which he warned that "oppressive" regimes like the one in Iran could not last.

"The USA is watching very closely for human rights violations!" he tweeted on Sunday, before accusing the government of cutting off the Internet to stop word of protests spreading -- an apparent reference to Tehran's efforts to limit access to social media.

Trump's approach is rooted in the belief of many Republicans that Obama's strategy did not do enough to fan protests against an enemy government and allowed Iran to invest the proceeds of sanctions relief under the nuclear deal to bolster its influence throughout the Middle East.

But it assumes the protests in Iran represent a direct uprising against the government and the radical clerical regime, a reading of the situation countered by many analysts, who see domestic and economic, rather than ideological motivations, driving the demonstrations.

And the President's concern for human rights seems selective, since he made no such demands of autocratic leaders he has cozied up to, including Xi Jinping of China, Vladimir Putin of Russia and Rodrigo Duterte of the Philippines.

Still, the instinctive, forceful and less-nuanced approach of Trump contrasts with the more circumspect strategy pursued by Obama after Green Revolution protests broke out in response to a disputed election win by President Mahmoud Ahmadinejad.

Obama's response reflected his tendency to plot how splashy presidential gestures would play out several moves in advance — and how they would be received elsewhere in the world, outside Washington's political echo chamber.

Critics say Obama's method led to hesitancy and underestimated US influence. But it contrasted with Trump's visceral reactions, which his detractors see as a symptom of rashness and a lack of depth but his supporters view as a refreshing willingness to wield American power more forcefully.

When protests took place in Iran in 2009, Obama did raise concerns about violence and called for the right of protesters to be respected, but he also argued that by getting involved in the situation, the United States, given the historical baggage of its past interference in Iranian politics, would only make matters worse.

A couple of days later, Obama said Washington could no t be "seen as meddling" i n Iran, given its tortured history with the country, in what aides said was an attempt to avoid being seen as calling for regime change in a way that could give Ahmadinejad an excuse for a crackdown.

At the time, Obama's caution was seen as a sign of foreign policy realism following the Bush administration's idealist approach to the Middle East, which sparked chaos after the toppling of Saddam Hussein in Iraq.

Dennis Ross, who was a National Security Council official under Obama and veteran Middle East peace negotiator, told CNN on Monday that, in retrospect, the initial caution shown by the last White House was a "mistake," even though it was based on requests from Green Revolution leaders to "keep it cool" in order to deprive Tehran of the opportunity to claim the protests were foreign-inspired.

"I think we should have made it clear that, in fact, the world was watching," Ross said, adding that Trump was striking the "right tone."

Among critics of Obama at the time was Mike Pence, then a Republican congressman and now the vice president, who said he appreciated that Obama was troubled by the violence but called for a much tougher line.

A few days later, Obama did adopt a harsher stance, after heartbreaking video of the shooting death of a 26-year-old Iranian woman named Neda Agha-Soltan, went viral. He said he was " appalled and outraged by the threats, beatings and imprisonments of the past few days."

But Obama's new tone came too late to defuse a new Republican critique that lingers to this day: that he stayed quiet in the face of tyranny just to appease Iranian leaders.

Republican presidential nominee Mitt Romney took up the cry in the 2012 campaign.

"When millions of Iranians took to the streets in June of 2009, when they demanded freedom from a cruel regime that threatens the world, when they cried out, 'Are you with us, or are you with them?' the American president was silent," Romney said.

Republican Sen. Lindsey Graham, of South Carolina, made a similar argument Sunday.

"If I were Trump, I'd do the exact opposite of Obama," Graham said on CBS' "Face the Nation." "Obama said, 'I don't want to get involved, I don't want to mess up the chance of getting that deal with Iran.'"

Such Republican assessments not only ignore Obama's progression toward a tougher line on the protests, but also fail to take into account that less than two months after they erupted, he led the leaders of France and Britain in exposing a secret Iranian nuclear fuel plant when they met at the G20 summit in Pittsburgh.

The Obama administration subsequently worked to impose the most punitive global sanctions ever imposed on Iran, a step his supporters say so damaged the Iranian economy that its leaders were forced back to the negotiating table.

In many ways, the different approaches of the two administrations reflect contrasting conclusions about what the protests in Iran actually mean and how US policy can best be shaped to weaken the potency of a longtime enemy.

Reza Marashi served in the Office of Iranian Affairs at the State Department in 2009 and says the Obama administration concluded after a wide-ranging assessment that the protests did not threaten the regime.

"There are a variety of factors that would have to align in order for protests to become a revolutionary type situation instead of a continuation of the longstanding civil rights movement in Iran," he said.

Factors the Obama team took into account included the legitimacy and efficiency of the government, the unity of elites and the regime's lopsided ability to use force to end the protests.

It also looked at the capacity of protesters to unite behind common leaders and ideology at a time of mass disconnect with the government.

And despite Trump's tough tone, the picture inside Iran appears little changed now, meaning that despite the new American approach, Washington's capacity to influence how the protests play out remains limited.

"When I look at the situation as it exists right now, there are a variety of factors on both sides that currently are not there in order to facilitate a revolutionary situation," Marashi said.