Yes, you can easily copy a previously sent campaign using the Clone option by following the steps below. You will clone campaigns from the Campaigns dashboard.

How-To

Navigate to your campaigns dashboard. Locate the advanced search icon on the page.
Click open advanced search, select Sent for the Status filter. You can click to deselect any other statuses. Then click the blue Search button (lower-right) of advanced search pop-out to return results.
Hover over listed campaign in Sent status that you want to copy to expose a View button with a drop-down. Click open the drop-down and select Clone.
A pop-up will open. Provide a new name for the campaign. Then click Ok.

The clone will appear in your Campaigns dashboard as a draft. Hover over it to select the "Edit" button to make changes to the new clone.