You can resend a campaign, but only to constituents who have not opened it yet. See this article for more "Can I resend an email campaign to those who did not open?"

You can also make an exact copy of the campaign and resend that to whatever email lists you wish. To copy a campaign, highlight that campaign on the grid and from the Actions menu select Copy Campaign. A new window will open to allow you to name the campaign (it defaults to Copy of Campaign Name) and all the original information, recipient list, and template will be included in the new campaign. You can resend to the same list or you can make any changes needed to the campaign info, recipients, template, and schedule.