The U.S. dollar has been sliding in the run-up to a widely expected interest-rate cut from the Federal Reserve on Wednesday and, depending on the size of the Fed’s move, it could end up weakening further — or it could be a buying opportunity.

The dollar weakened and the yen hit its highest level in more than a year on Monday, as market participants increasingly expected an oversized rate cut by the Federal Reserve later this week. The dollar fell to as low as 139.

Another point to consider is Dollar General's ( DG 1.18%) outperformance since the July 6, 2015, acquisition. It's Dollar Tree's most direct competitor. Dollar General's total return of 16% from then to now outpaces Dollar Tree's 17% drop in total return.