Democrats are banking on another backlash against Senate Republicans for leaving town without extending unemployment benefits.

For the second time in March, GOP senators are blocking swift passage of an extension to unemployment insurance. Earlier this month, Sen. Jim Bunning (R-Ky.) objected to a quick vote on a $10 billion, monthlong extension, only to relent under Democratic criticism and see half of his GOP colleagues vote to clear the package for President Barack Obama's signature. This past week, Sen. Tom Coburn (R-Okla.) blocked repeated Democratic attempts to vote on another monthlong extension with a cost of $9.2 billion. Without the extension, the benefits are set to expire on April 5. Democrats said that...