Intervention supported the yen but only bought time; the real support would come from a BOJ rate hike in September and a hawkish signal for further hikes, which would strengthen the currency.
The U.S. is worried about Treasury yields and intervened partly to prevent Japan, the biggest Treasury holder, from selling more U.S. Treasuries; if Japan sold, it would push U.S. yields higher, and verbal intervention or intervention only helps for some time, leaving Treasury yields vulnerable.