CAIRO — In Morocco, it would tip a delicate political balance. In Jordan, it could prevent American diplomats from meeting with opposition leaders. In Tunisia, it could make criminals of a political party seen as a model of democracy after the Arab Spring.
Of all the initiatives of the Trump administration that have set the Arab world on edge, none has as much potential to disrupt the internal politics of American partners in the region as the proposal to criminalize the Muslim Brotherhood, the pre-eminent Islamist movement with millions of followers.
“The impact would be great,” said Issandr El Amrani, an analyst with the International Crisis Group based in Morocco, where a Brotherhood-linked party won the last election in October. “It could destabilize countries where anti-Islamist forces would be encouraged to double down. It would increase polarization.”
At issue is a proposal floated by Trump aides that the 89-year-old Brotherhood be designated as a foreign terrorist entity. The scope of any designation remains unclear, but its potential reach is vast: Founded in Egypt, the Brotherhood has evolved into a loose network that spans about two dozen countries. It has officially forsworn violence.
For President Trump, the designation debate is an election promise made good. He has made no bones about taking an approach to the Middle East that is narrowly focused on counterterrorism, and that plays to domestic supporters who view all Islamist movements — or even all Muslims — as potentially hostile.
In much of the Middle East, though, the rapid pace and embattled rollouts of Mr. Trump’s early orders have induced anxiety. Now many are following the potential indictment of the Muslim Brotherhood as a harbinger of things to come.
“The Obama administration moved us away from the ‘clash of civilizations’ narrative,” said Emad Shahin, a dissident Egyptian academic who lectures at Georgetown University. “Trump is taking us deeper into it.”
Not all are unhappy about the move to list the Brotherhood.
One leader the designation would surely delight is President Abdel Fattah el-Sisi of Egypt, the former general who has led a harsh crackdown on the Brotherhood since the military ousted a Brotherhood leader, Mohamed Morsi, as president in 2013. Saudi Arabia and the United Arab Emirates also would support it.
But in countries where Brotherhood-linked parties are prominent in Parliament or are in power, experts say a sweeping indictment could have serious implications for domestic politics, American diplomacy and the broader fight against Islamist extremism.
In Jordan, a crucial ally in the fight against jihadist groups, Islamists constitute a small but significant bloc in the Parliament. Tunisia’s Ennahda party, which has won wide praise for its democratic engagement and moderate stance since 2011, might be shunned. The prime minister of Morocco, technically, could be considered a criminal.
“You would throw many babies out with the bath water,” said Gerald M. Feierstein, a former United States ambassador to Yemen, now at the Middle East Institute in Washington.
The initial momentum toward such a designation appears to have slowed. A leaked assessment by the Central Intelligence Agency said isolating the Brotherhood would serve only to empower jihadist groups; some experts doubt that a broad designation would pass legal muster.
But the very fact that the ban is under consideration by Mr. Trump’s aides is being taken as an ominous sign in a region where religion and politics are carefully, and often precariously, balanced.
The proposed designation has also reaffirmed Mr. Trump’s apparent embrace of Mr. Sisi, who has weathered a barrage of international criticism for his country’s dismal human rights record in recent years. Mr. Trump has hailed him as a “fantastic guy” with whom he shares “good chemistry.”
Since an initial meeting at the United Nations in September, the two leaders have spoken several times by phone — Mr. Sisi was the first foreign leader to congratulate Mr. Trump on his victory in November — and now a visit to Washington by Mr. Sisi is under preparation.
Egypt wants the United States to resume a military financing program, frozen by President Barack Obama in 2015, that helps it make billions of dollars in purchases of big-ticket weapons like F-16 warplanes and M1A1 Abrams tanks.
More than anything, though, a handshake in the White House for Mr. Sisi would offer a stamp of legitimacy to a leader who had been kept at arm’s length by Mr. Obama.
Tens of thousands of Mr. Sisi’s opponents languish in Egyptian prisons, human rights workers are routinely harassed, and his security forces have faced accusations of extrajudicial killings.
To some, it suggests Mr. Trump is set to take an approach in the Middle East that will not just tolerate strongmen and monarchs but also actively seek to embrace them — a throwback that evokes American alignment with autocrats like the shah of Iran in decades past.
“It’s easy to say you will stand by your friends,” said Mr. Feierstein at the Middle East Institute. “But authoritarian regimes are always brittle, always fragile. We thought we would stand by the shah of Iran until the day he got on an airplane and left the country. Now what do we have to show for it? We have 40 years of not being able to have a relationship with Iran.”
Brotherhood officials insist that the Trump administration has gotten it wrong. In a letter smuggled from the high-security Egyptian prison where he is being held, the Brotherhood spokesman Gehad el-Haddad admitted that his party had made serious mistakes during its yearlong stint in power in Egypt from 2012 to 2013. Citing the “hard-learned lessons of the Arab Spring,” he said the Brotherhood had failed to heed loud opposition from millions of Egyptians who disliked Mr. Morsi’s actions.
But, he insisted, the movement renounced bloodshed. “Our flaws are many,” he wrote. “Violence is not one.”
In other places, the reality can be harder to pin down. By nature secretive, the Brotherhood takes different forms around the world. In some places, its members have condoned or committed violent acts. Its Palestinian offshoot, Hamas, carries out suicide bombings; in Egypt, angry young supporters have been accused of attacking Mr. Sisi’s security forces.
But that does not make terrorists of the many millions of people who support the Brotherhood’s political ideology across many countries.
One route for the Trump administration could be to narrowly designate specific Brotherhood branches as terrorists, said Mokhtar Awad, an expert on the group. But it would be better still, he argued, to “engage in a battle of ideas.”
The debate could prove an early lesson for the administration in doing business in the Middle East, which has long resisted broad-brush prescriptions. Unpalatable as its ideas may be to Trump officials, the Brotherhood may become just one of many factors they will be forced to grapple with.
“We engage with the Brotherhood knowing they are problematic actors, but they are also a reality,” said Michael Wahid Hanna of the Century Foundation. “And the alternative — ignoring or repressing them — leads to a very bad place.”
Correction: February 20, 2017
An earlier version of this article misstated the year that President Barack Obama froze Egypt’s military financing program. It was 2015, not 2013.