Re: "The .. crime we uncovered here could threaten the integrity of our wildlife species in Montana"
This is true - obey the rules. Even if they will eventually damage the resilience of our ecosystem.
Species have been moving across those invisible national borders since the dawn of time and still do, naturally and artificially. One of the main reasons is climate change (there has actually been quite a lot of it). As climates change, flora and fauna have to move. Even trees move, by surviving and dying out in different places. As the pace of climate change increases, we will need to help species move.
In the last few centuries scientists catalogued species within national boundaries, and declared them to be 'native'. But nature never stops changing. The Canute option of only planting so-called 'native' species and wiping out nasty foreign invaders, coming over here, nicking our sunshine and soil, is crazy. That's not how nature works, and we need to learn from nature.
Yes, there have been some notoriously rampant species like Japanese knotweed and cane toads (nature sorts this out over time, but humans are impatient and panic). However species that are successful and aggressive are more likely to survive climate change. Red squirrels almost certainly will not in the UK, but greys are tougher little guys and probably will. Unless of course we wipe the greys out, the climate wipes the reds out, and we have none. Species that arrived from abroad before scientists drew the line in the sand have often done well: Buddleia is brilliant for butterflies and insect life, but isn't native to the UK. And it is an aggressive spreader.
The natural world copes with extreme period of climate by reducing diversity and running with a smaller mix of resilient predator and prey species. We need to learn from that too.
Some species need specific plants, some will adapt, but the majority just need plants that do the basic pollen, nectar and seed thing, regardless of what passport they hold. One thing is certain, they will have to be more resilient than most of our current 'natives' to survive. If we stick with 'native' species, most of them will die as the climate changes and the place will start to look like Mars in the summer.
And as for rewilding with things that died out hundreds of years ago - that is no different from the introduction of entirely foreign species. It's not a long-missing part of the puzzle, as humans and other species have changed the mix so much already. It sucks cash from much better projects but won't stop until a protective mother boar kills a child or two.
Australia probably needs to change its flora more than most countries as Eucalyptus trees and fire don't mix. Elsewhere, we need to plant species that provide us with local seasonal food, whilst ensuring that solar farms are hybrid - panels with underscrub or crops. So while it is a good idea to keep fire ants out, the puritanical protection of 'native species' and rewilding will both eventually be recognised as catastrophically bad ideas a few years and a few million quid down the line. Just wait and see.