Not specific to .US really
Pretty much every new gTLD that can be registered on "promotional" first year prices below .com/.net/.org harbors a large than usual proportion of phishing domains and suspicious things, because one of the sole operational criteria for phishers registering disposable domains that might have useful lives of only hours or a few days, in bulk, is the cost per unit.
".us" is in much the same situation because I am seeing promotional prices of $4.50 to $5 per domain for the first year.