Donald Trump Gushes Over DHS Chief Markwayne Mullin's Wife's Looks

President Donald Trump is clearly impressed with his newly confirmed Homeland Security Secretary Markwayne Mullin ... not just when it comes to his work -- but by his wife, too.

Mullin's swearing-in ceremony took place at the White House on Tuesday ... where Trump gave a nod to his family, saying he wouldn’t be there without them.

But then, Trump zeroed in on Mullin's wife, Christie ... gesturing toward her and their kids, saying, "And that goes especially for mom, who looks like she's about 22 years old. I see these kids, but she looks very young.”

Christie -- who is 47 -- was clearly flattered … laughing and placing her hand over her heart.

Trump went on to praise the "great couple" -- who met in high school and have been married for nearly 29 years -- congratulating them both and shaking their hands.

Moments before … the prez even brought Mullin’s son, Jim, up to the podium, grabbing his arm and giving his bicep a squeeze while joking to the crowd, “Don’t wrestle him.”