Call this pouncing all you want, but it's smart politics, especially given the initial fumbles to define Harris after The Anointment. Trump and his team unwisely went after her identitarian claims, which backfired to some extent at an event that could have provided Trump with some narrative cred for political courage otherwise. Also, Harris' visibility has already largely left her defined in the public sphere, a situation where a smarter strategy would have instead focused on policy failures in the Biden-Harris administration entirely.
But that isn't true of Walz, who barely has had any national exposure outside of the Minneapolis riots. A Morning Consult survey shows just how undefined Walz is, even to fellow Democrats, before being picked to run on the presidential ticket. He's literally the least known of the rumored Veepstakes short-listers (via Andrew Malcolm):
This is yet more evidence of poor choice in the Veepstakes decision. Josh Shapiro would have been harder for Republicans to define in the election cycle when two-thirds of voters already know who he is. That's even more true of Gretchen Whitmer, although her negatives are slightly higher than Shapiro's. Furthermore, both Shapiro and Whitmer come from must-win states (PA and MI, respectively) where they are already much more well-known than they are overall on a national basis. Choosing either one of them would have largely left Republicans without a target other than Harris.
Kamala STORMS off after Journalist DRILLS her over Trump debate