Sameeha Alkamalee Jabbar of Orange County, Calif., takes part in a naturalization ceremony in Los Angeles in September. More than 700,000 immigrants are now waiting on applications to become U.S. citizens, a process that in many parts of the country now takes a year or more. (Amy Taxin/AP)

More than 700,000 immigrants are waiting on applications to become U.S. citizens, a process that once took about six months but has stretched to more than two years in some places under the Trump administration.

The number of immigrants aspiring to become U.S. citizens surged during 2016, increasing 27 percent from a year earlier as Trump made cracking down on immigration a central theme of his campaign.

At first, the 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 a 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 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 Thursday that Central American migrants headed north in a caravan should return home and apply for U.S. 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.

But immigrants generally must be legal permanent residents of the United States to apply for citizenship, and obtaining 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 a U.S. 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 get more eligible voters to the polls.

Keeping potential citizens from voting could have an effect on the midterm elections, but it could also drive more of their relatives and friends to the polls.

“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.

— Associated Press