Weeks of falling gas prices are dulling what had previously been a sharp Republican weapon, giving Democrats another glimmer of hope ahead of the midterm elections. Months ago, sky-high gas prices were a major reason why Democrats’ prospects looked bleak. But as candidates hit the homestretch ahead of the Nov. 8 midterms, the lower gas prices are giving reasons for Democrats to think they can be more competitive. “It takes a lot of the effectiveness out of a cudgel when people aren’t seeing and feeling it as much,” Democratic strategist Eddie Vale said of gas prices. Since hitting a June...