Please show me exactly what law he broke.
Trump Jr. didn't promise anything, or offer to do anything. Even if this was a direct Kremlin representative (it wasn't), they didn't promise anything or offer to do anything either, apart from show Trump Jr. the information they had gathered.
Receiving information isn't a crime. If it were, then we could spam info at each other to initiate a malicious prosecution whenever we wanted. Sure, there are laws against taking money from a foreign power to finance a campaign. But that's not what we're talking about here. "Collusion" has become this nebulous concept that isn't limited to illegal conduct. Exchanging information isn't illegal, even if it's illegally procured.
The email from Rob Goldstone said that the Russian government supports Trump's candidacy. But that isn't a crime on the behalf of anyone from Trump's camp, and that doesn't mean you need to build a firewall against anyone who might have some alleged ties to all other foreign governments. You can't take money from them. You can't promise them anything in return for their support. But if someone offers to send you free information damaging to Hillary, you don't have to turn them away just because they're wearing a Russian hat.
In contrast, Hillary Clinton actually
accepted money from a foreign power for her campaign, which IS a crime.