In June 2009, following a presidential election in Iran won by hardliner Mahmoud Ahmadinejad over the more moderate Mir Hussein Musavi, protesters took to the streets of Tehran questioning the results and demanding the removal of the victor. The student-led spontaneous reaction grew into the largest demonstrations in Iran since the 1979 revolution, becoming increasingly violent, and resulting in a shaken government using deadly force to contain what became known as the Green Revolution or Persian Spring.

There was a brief period when it appeared that President Obama was going to weigh in on the side of the protesters, but in the end, he held back, a decision that was widely criticized in the aftermath as a missed opportunity to back those calling for a return to democracy in Iran.

Now, in the most serious confrontation with Iran’s theocracy since 2009, President Trump has, to his credit, taken a different tack, tweeting his support for demonstrations that have grown larger and more volatile over the past week in a number of Iranian cities. People are venting frustration over economic woes — most immediately, a sharp rise in food prices — and a lack of political reforms.

President Hassan Rouhani of Iran, a relative moderate who was elected in 2013, had pledged that the 2015 nuclear agreement with the West would end stringent sanctions and restore financial stability to the country. But while Iran received billions of dollars as a result of the agreement, much of it went to the powerful Revolutionary Guard and helped pay for Iran’s military campaign in Yemen and for Hezbollah’s defense of Syria’s regime in that country’s brutal civil war.

Will vocal U.S. calls for democracy in Iran help the cause of the dissidents or, as critics fear, allow the mullahs in Tehran to blame the unrest on the U.S. and, of course, Israel?

On Monday, Iran’s Supreme Leader Ayatollah Ali Khamenei asserted that foreign enemies were responsible for the protests, which have claimed at least 20 lives. But such excuses may well be viewed within a skeptical Iranian society as the falsehoods they are.

President Trump, who has consistently spoken out against the Iranian regime as evil and a threat to Israel and the entire region, has the potential to do serious damage to the Iranian theocracy at a time when so many of the country’s young people are deeply frustrated with the status quo. But presidential tweets are not enough. Congress should be encouraged to threaten renewed and tougher sanctions if Iran’s leaders use violence against the protesters. And the U.S. should pressure our European allies to forego financial gain in dealing with Iran and speak out as well for human rights, non-violence and an end to corruption.

This could be the moment when Iran’s brutal theocracy and role as world leader in exporting terror is seriously weakened, if not toppled, largely from within — with the help of a purposeful and well-orchestrated effort in Washington.