Beyond the additional security present at the ceremony, the Knavs followed the same process of tests, interviews, and paperwork that every other citizenship candidate has to complete.
Under US immigration law, Melania's parents would need to have had green cards for at least five years before they could apply for citizenship.
Melania Trump - who has been vacationing with her husband U.S. President Donald Trump in Bedminster, N.J. - did not accompany her parents. He confirmed that the first lady sponsored their green cards.
"NOT ACCEPTABLE!" Wildes told The New York Times "I suppose" the Knavses obtained citizenship through chain migration, and called it a "dirtier" way of describing family-based immigration, "a bedrock of our immigration process when it comes to family reunification".More news: Twitter CEO not banning conspiracy theorist Alex Jones
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President Donald Trump's parents-in-law have become United States citizens in a private ceremony.
Melania Trump became a US citizen in 2006 after marrying Trump the year before.
Wildes wouldn't comment on how the Knavs received their green cards or citizenship Thursday, but criticized the Trump administration's immigration policies to CNN.
They raised Melania in the rural industrial town of Sevnica while Slovenia was under Communist rule.
Amalija is 73. The first lady, born Melanija, changed her name to Melania Knauss when she started modeling.