Handlebar knobs rusted and stuck seem to be all too common with the Trail 70. I already broke one knob on the blue bike and tore up the threaded slug in the good right bar trying to save it. The left bar is already bent so trying to get it apart is more the experiment of learning for the next time rather really saving anything this time. It seems just as stuck and the one I broke. I had tried penetrating oil(s) and heat with no success. The rusty threads are just too far from the surface to get at. So this is my next try. A bucket full of Evaporust. A good soak should get all the way to the threads, hopefully. I hate to use most of a whole bottle, but remember if it doesn't turn black you can reuse it.
About 3 hours later I pulled it out.
A couple of decent whacks can't hurt anything.
I used the groove joint pliers to "worry"(tighten-loosen-tighten-loosen) and by goodness it broke free.
It was hard to tell if the solution really got deep into the threaded joint, but I call that success.