Lindsey Graham says wearing a mask’s not just being patriotic like President Trump has VERY belatedly said — it’s also just plain smart … but he’s got reasons why he wasn’t either the other night.

We got the South Carolina Senator on Capitol Hill Thursday, and he explained why he and POTUS were spotted mask-free at Trump’s D.C. hotel Monday night … mere hours after 45 finally supported wearing one on Twitter.

Graham tells us they had all just had dinner — and obviously they can’t cover their faces while eating — but more to the point … he claims they’d all just been tested.

Listen carefully though … the Senator balks a bit when our guy asks if everyone in the room at the Trump hotel — where he was seen yukking it up with Congressional hopeful Madison Cawthorn — was also tested.

Regardless … Graham has recently been pushing for SC residents and all Americans to mask up in order to turn the corner on surging COVID-19 cases. His state is currently seeing a spike in hospitalizations, as are so many others.

As we reported … Trump announced Thursday that the RNC in Jacksonville was canceled because of COVID concerns.