Bower apparently does not work for installing Bootstrap into a Visual Studio project any more:
https://developercommunity.visualstudio.com/content/problem/134643/bootst
The simplest way is to use the NuGet console.
simply navigate to:
Open VS >> Tools menu >> NuGet Package Manager >> Console Command.
Alternatively: Options >> NuGet Package Manager >> Package Sources dialog box.
Once the console appears at the bottom page, type:
PM> Install-Package bootstrap -Version 3.3.7
If this gives you any issues or helps, please let me know.