Grassley is a straight-talker who doesn't let the national party dictate his positions. On the other hand, he also doesn't let the national interest get in the way of his state interest. Great if you're an Iowan, not so great if you're from one of the other 49. But that's how representative democracy is supposed to work. It's expected that everybody tries to work his or her own angle, and it's everybody else's job to keep each other honest. You can't expect Grassley not to try to squeeze in that extra yard for Iowa.
Normally Grassley is spot-on, as he was in this case, but occasionally he deviates from plain old common-sense rationality, and it usually has something to do with corn. He has argued against all reason that ethanol from corn can supply a substantial part of the nation's energy without raising gas prices or food prices (wrong; it will raise both). Now he's raised the old bogeyman that "marijuana leads to harder drugs". The first question is where's his evidence? For four decades people have been repeating this tired old saw, without producing data to back it up.
In economic terms, marijuana is often compared to corn. Since the mid-1980s in the U.S. marijuana has been a bigger cash crop than corn. From a Libertarian standpoint, what we have now is a marijuana prohibition that criminalizes a harmless substances with medical benefits and creates a criminal class that is currently terrorizing our southern border. But I can't help but think that legalization would lower the amount of acreage dedicated to corn production and damage the corn lobby. Coincidence?