The obvious explanation is that triage time is upon the DSC. If it cannot close the gap Cotton has opened on the seriously weak and wounded Pryor, it will be time to stop wasting precious resources on him and rush them to another race –one of a dozen that might go GOP but which might also be saved with a 100% effort.
More than a few Democratic senators have to be whispering to Reid et al that it is time to cut their losses in Arkansas and concede the state to the GOP as they have West Virginia and South Dakota. Among those whispering the most loudly, embattled Mark Begich in Alaska, Mark Udall in Colorado, Mary Landrieu in Louisiana, Jeanne Shaheen in New Hampshire, Mary Landrieu in Louisiana, and Jeff Merkeley in Oregon. Even Al Franken may be worried about blowing scare resources that should be used defending their seats and the D’s majority rather than pouring them into an unwinnable race in Arkansas.
For a complete scorecard on the 2014 Senate races, see this post from two weeks back. The numbers have only gotten worse for Democrats since then, especially with Braley imploding in Iowa and Merkeley’s Oregon the site of what Politico is calling Obamacare’s “biggest technological disaster.” The Senate map is terrible for Dems and getting worse by the day. How long do they waste money on Mark Pryor’s Weekend at Bernie’s campaign?