Libertarian presidential candidate Gary Johnson took a jab at Donald Trump on Thursday, promising not to deport the billionaire's Slovenia-born wife if he's elected president.

"While Donald Trump is running on a platform to deport 12 million people, apparently including his own wife, Johnson-Weld stands for allowing people in Melania's circumstances to stay and, over time, become citizens if they learn English, pay their back taxes and pay a fine," Johnson's campaign wrote in a statement amid new reports that raise questions about Melania Trump's immigration history.

The Johnson campaign also welcomed "other glamour models from around the globe to come to America and make it an even more beautiful country than it already is."

Both Johnson and his running mate, former Massachusetts Gov. Bill Weld, have sharply criticized Trump's proposed plans to build a wall along the U.S.-Mexico border and deport 11 million illegal immigrants if he's elected president. Weld likened Trump's deportation plan to the killing of Jews in Nazi Germany during an interview in May.

"Insanity comes to mind," Johnson once told CNN when asked about Trump's immigration proposals. "We should make it as easy as possible for someone who wants to come into this country to work to get a work visa."

In their statement, Johnson and Weld promised "sensible, pro-growth, freedom-loving" immigration reform and economic policy.