American Muslims can expect a phone call soon from Khizr Khan. On Sunday (Nov. 6), he will remind them to get to the polls on voting day through a robo-call to 500,000 registered voters, organized by the Council on American-Islamic Relations (CAIR), a Muslim advocacy group.

The grieving father of a slain American Muslim soldier made a splash at the Democratic National Convention in July when he delivered a searing speech excoriating Republican presidential candidate Donald Trump for his anti-Muslim and, according to Khan, anti-constitutional views. In the months since, Khan has proven to be an effective surrogate for Hillary Clinton’s campaign, especially when it comes to mobilizing American Muslims. The campaign recently launched a powerful ad featuring Khan asking Trump whether his son Humayun, who sacrificed his life in the Iraq war, would have a place in Trump’s America.

While American Muslims comprise a mere 1% of the country’s population, their votes may play an outsized role in this election. The Muslim population is concentrated in several key battleground states including Florida, Virginia, Michigan, and Ohio, where the race is tight and will likely be decided by small margins.

Muslims’ outsized influence is not without precedent. They leaned Republican before the election of George W. Bush to the White House, in part due to conservative social values; 72% voted for Bush in 2000. The Muslim swing vote may have been the deciding factor in Florida—and ultimately the election—where margins were razor thin and Bush carried the state by a few hundred votes.

In the years since, the Muslim vote has drifted leftward as wars have intensified in the Middle East. Trump’s declaration that “Islam hates us” and his proposal to ban Muslims from the US clinched the deal between Muslims and Democrats.

Khan’s speech at the DNC and subsequent calls for action among Muslims appear to be working: Muslim activist and commentator Wajahat Ali dubbed American Muslims “Khizr Khan voters” in a recent column, arguing that Trump’s Islamophobia, highlighted by Khan, has boosted Muslim political engagement.

In June, CAIR reported that voter registration among American Muslims was up 30% from 2012. The US Council on Muslim Organizations, another advocacy group, has spent the past year registering thousands of Muslim voters across the country. On Nov. 2 it announced that a record-breaking 1 million Muslims are currently registered to vote Tuesday. A CAIR survey found that 86% of Muslims intend to vote for Clinton.

Muslim Americans have stomached Clinton’s candidacy despite her questionable rhetoric about Muslims, which focuses heavily on national security, and her hawkish foreign policy.

“Trump’s bigotry was a blessing in disguise,” Zahir Bukhari, a member of the Islamic Circle of North America who has been campaigning for Muslims to get out the vote, told the Wall Street Journal.

CAIR executive director Nihad Awad echoed the sentiment: “I usually don’t thank the candidates but I’d like to thank Trump for energizing the Muslim community in an unprecedented fashion.”