The Montana legislator was one of 18 U.S. Senators who were down at the southern border this past week -- surveying what they're calling one of the biggest crises facing the country today ... this in light of the fact President Biden hasn't been down there himself just yet.

Sen. Daines stepped to a podium Friday and delivered remarks about how the issue of illegal immigration -- and the ramifications of that -- have affected his state. In a bizarre train of thought, he said one of the hits Montana has taken from this is ... more potent/fatal meth.

No, we're not kidding ... the guy appeared to be harkening back to a time in Montana when meth was American-made, and not nearly as strong as it is today, via Mexican drug lords.

It almost sounded like he was saying, "Remember good old-fashioned American meth?" That's certainly the vibe, anyway -- and you can even see some of his comrades chuckling behind him, including Sen. Mike Lee ... who's looking around with a major WTF face.

The Republicans down there now have been cruising along the Rio Grande River and putting on a big show at different border sites ... claiming things are bad as the surge of migrants continues at a startling pace. The problem is certainly real, there's no question about that ... but their song and dance demonstration is a bit silly. They're also kinda reveling in this visit a bit too much, we'd argue, taking photos of themselves in boats with bulletproof vests.

There's also Ted Cruz's live, on-the-scene video ... which has also made the rounds. He's reporting from the banks of the Rio Grande, and claims to have seen Mexican cartels sneaking in with his own eyes -- saying they heckled him as they passed.