NATO is formidable even without the U.S.:
Population: 632 Million (US=348M, Russia=143M)
Military Budget: $610 Billion (US=$900B, Russia=64B)
Active Personnel: 2.1 Million (US=1.4M, Russia=1.3M)
Tanks: 6,855 (US=4,640, Russia=5,750)
Aircraft: 8,036 (US=13,043, Russia=4,292)
Navy: 671 (US=480, Russia=375)
Nuclear Weapons: 515 (US=5,177, Russia=5,600)
This is current state and with Europe modernizing and re-arming, these figures will certainly increase. It also wouldn't surprise me if it expands to include Japan and South Korea.