Hi there,
I can only imagine what your last couple of weeks have been like!
Is Senator going outside at all? Just in your backyard? It should be fine for him to go outside as long as he doesn't go anywhere there could have been unvaccinated dogs like public parks, roads etc. The sooner you introduce him to new things and new experiences the better.
Are their any friends with dogs that you could take him to visit? As long as they have had all their shots and are nice friendly dogs it would be really great for Senator to socialise. The most crucial time for dog socialisation is between 4 and 14 weeks old and so this it is vital that they are exposed to as many things as possible.
When first introducing anything to a young dog just do it gradually and make sure they don't feel forced into something that may terrify them. Encourage any forward behaviour they show and ignore any fearful behaviour like cowering. Its difficult as you will feel like comforting them when they are scared, but by doing this you are telling them that they should be scared.
With going outside, can you leave a door open to the backyard so he can go out when he wants and at his own pace? Make it fun for him - take out his favourite toy and make it into a game
Hope this helps,
Kate