The key is the different messaging aimed at each Republican. In a mailer obtained by the Newark Star-Ledger (shown above), PMUSA slams MacArthur as a politician who "raised taxes and increased spending EVERY SINGLE YEAR" he served on the Randolph Township Council—the sort of hit Republicans frequently use against one another in primaries.
The argument against Lonegan, on the other hand, is very reminiscent of the tactics Claire McCaskill used to boost Todd Akin. Indeed, the very same flyer also complains that "conservative Steve Lonegan is just too extreme for New Jersey" and accuses him of wanting to eliminate the Department of Education and defund Planned Parenthood. These, of course, are the kinds of things that GOP primary voters actually like!
Unfortunately, we don't have copies of the TV ads, but the folks at PolitickerNJ have seen them, and they're structured along similar lines, with MacArthur again getting attacked as a tax hiker. The Lonegan spot, though, goes even further, criticizing him for opposing federal disaster aid and saying that New Jerseyans should "suck it up" after Hurricane Sandy. While ultra-conservatives often loathe disaster relief when it goes to folks other than themselves, is Lonegan really a hero to the base for dumping on his own state after a major tragedy?
In any event, PMUSA definitely isn't copping to a ratfuck—no one ever does, publicly. That's always both the smart and necessary move, since you never want to give folks on the other side even more ammunition to accuse you of meddling. Of course, MacArthur's campaign is already doing just that, claiming "Republican primary voters are going to see through it," but we'll know next week whether or not this worked.