Absolutely! If you choose to purchase templates through the Creative Shop, the template will appear under "My Templates" and you can use that template as many times—and for as many ads—as you'd like.
Once you've uploaded a creative file, it will show up under "My Creatives." Then, each time you create a new campaign, you can select any of your creative files to attach to that campaign without the need to upload the file again.
Do you have an Agency or Organization Account? Ads you create for a particular advertiser can only be reused for that same advertiser. To read more about how each client's assets are separated in the system: Why do I need to associate each campaign to an 'Advertiser'?
Important Note:
As you upload each creative, you must chose whether that creative is 'Election Advertising' or not. Only creatives designated as 'Election Advertising' will appear as options for campaigns that are similiarly designated as 'Election Advertising.'