@Jenna **
No. If you apply and then leave, and then the visa is issued, you can still use it. But part of the visa application is uploading your plane ticket to Thailand. So if the embassy comes back and asks you to prove where you are and you cannot prove you are still in the US, they could possibly cancel your visa application. It's unlikely but possible.
Also you cannot activate the visa once you are in Thailand, so you would have to leave and return in order to activate your visa.