Restoring and Improving Merger Enforcement Act of 2018 This bill revises the standard for determining whether a proposed corporate acquisition would substantially lessen competition. Specifically, the bill establishes that a court may consider a claim that the acquisition would increase efficiency only if such increased efficiency (1) is verifiable, (2) could not be accomplished without the acquisition, and (3) would promote competition. The bill also places the burden of proof on the defendant claiming that increased efficiency will eliminate the substantial lessening of competition that would result from the proposed acquisition.