ISP's could block the common ports Bitcoin uses (but that would likely break a lot of other applications), they could potentially blacklist certain IP's, but because of the decentralized nature of Bitcoin this would likely only affect discovery in a minimal manner. ISP's could also inspect packets to determine if the traffic is Bitcoin related, but potentially something like TOR could prevent that inspection, if enough ISP's inspect & block Bitcoin TOR would likely not be of help (as it simply protects the transit of data, not the entry/exit).
BGP is also a pretty serious vector for a bad actor ISP to utilize, check out the following article: https://www.theregister.co.uk/2017/04/11/evil_isps_could_dis...
Definitely a lot of ways BTC could be affected. Governments could also outright ban it and that would destroy the network as it would lose a huge amount of value as a serious asset.
It's not as simple as that. Due to things like carrier grade NAT, thousands if not millions of users and services use the same IPV4 address, so shutting down a specific IP would be equivalent to an authoritarian dictator censoring innocent users.