The long wait times have prompted some immigrant advocates to ask whether the delays are aimed at keeping anti-Trump voters from casting ballots in elections.
"People are motivated to participate, and they're being frustrated from being able to participate in the elections they're excited about," said Manuel Pastor, director of the University of Southern California's Center for the Study of Immigrant Integration.
The number of immigrants aspiring to become U.S. citizens surged during 2016, jumping 27 percent from a year earlier as Trump made cracking down on immigration a central theme of his presidential campaign. At first, the federal government kept up with the applications, but then the wait grew.
Backlogs are nothing new in the U.S. immigration system. It often takes years to receive asylum or to be deported. But naturalization - the final step to become an American citizen, obtain a U.S. passport and receive voting rights - had not been subject to such delays in recent years.
Now the average wait time for officials to decide on applications is more than 10 months. It takes up to 22 months in Atlanta and as long as 26 months in parts of Texas, according to official estimates.
Trump tweeted on Thursday that Central American migrants headed north in a U.S.-bound caravan should return home and can apply for American citizenship if they wish. "Go back to your Country and if you want, apply for citizenship like millions of others are doing!" he posted as thousands continued their trek through Mexico.
RELATED: Migrant caravan halfway through journey to U.S.
But immigrants generally must be legal permanent residents of the United States to apply for citizenship and getting a green card can take years - if a person even qualifies for one.
U.S. Citizenship and Immigration Services said the longer waits to naturalize are because of the surge in applications, not slower processing. The agency decided 850,000 cases in 2017, up 8 percent from a year before.
Despite "a record and unprecedented" spike in applications, the agency is operating more efficiently and effectively and "outperforming itself," spokesman Michael Bars said in a statement.
To become an American citizen, immigrants must hold green cards for at least three years, demonstrate good moral character and pass English and civics tests.
Citizenship applications typically rise before an increase in filing fees and during presidential election years as immigrants get excited about the prospect of voting and advocacy groups conduct widespread outreach to try to get more eligible voters to the polls.
Enrique Robles, 32, said he applied to naturalize as soon as he was eligible after living in the U.S. most of his life. When he didn't hear about the status of his application, Robles, who is originally from Mexico, started to worry.
More than a year later, he said, he was called to an interview where an immigration officer questioned whether he should have been issued a green card in the first place, a concern he was able to quickly dispel by explaining that his father had legitimately sponsored him.
"With this administration, it feels like they are looking for more possibilities to kick people out," said Robles, who took his citizenship oath in September.
Keeping potential citizens from voting could have an effect, but it could also drive their relatives and friends to the polls in greater numbers.
"The naturalization delays have a huge cost in stopping some people" from voting, but they "have a huge impact in motivating others," said Jeremy Robbins, executive director of New American Economy, a bipartisan group in support of immigration.
Competitive districts that have a large number of foreign-born residents are likely to be among those where naturalization delays could matter most. Those include districts in California's Orange County and in Texas and New Jersey, Robbins said.
At a recent naturalization ceremony in Los Angeles, some new citizens said the process seemed long to them, while others said it flew by in a matter of months. Key for many was being able to travel with an American passport and being able to vote.
Sameeha Alkamalee Jabbar, 38, who is from Sri Lanka, said the process took 10 months and at times she worried about the backlog. She wants to vote next month because "every vote counts" - and especially because her husband is seeking re-election to a school board seat in Orange County.
"This is home now," she said, wearing a stars-and-stripes hijab. "I love the United States of America."
Immigrant advocates recently filed a lawsuit in Los Angeles demanding records from the Trump administration on the delays. They questioned whether wait times were longer in electoral battleground states and said that could suggest voter suppression.
Juliana Cabrales, Mid-Atlantic director of civic engagement at the NALEO Educational Fund, which supports Latino participation in politics, said the group is focused on driving voter turnout in the midterm elections but will quickly pivot to encouraging immigrants to apply for citizenship if they want to vote for president in 2020.
"Right now, we're finding ourselves in this space, in places like Miami and New York, where processing times are 21 months," she said. "If you want to vote in 2020 you have to apply (to naturalize) now."