Roll Call newspaper -- Fix alum! -- broke the news Tuesday afternoon: The Democratic Senatorial Campaign Committee has stopped its TV advertising for the final three weeks in the Kentucky Senate race. That decision effectively leaves Democrat Alison Lundergan Grimes on her own and is rightly read as a sign that national Democrats believe the race is effectively over.

"The DSCC has now spent more than two million in Kentucky and continues to make targeted investments in the ground game while monitoring the race for future investments, but is currently not on the air in the state," confirmed a DSCC official.

The DSCC's decision to pull out of Kentucky, a race in which they had spent months insisting was closer than most public polls showed it, is a recognition that in a year in which the Senate map and the national political climate are tilted against them, the party's best chances to hold the majority now rests in trying to hold onto their endangered incumbents.

One Democratic strategist closely following the Kentucky race insists that Senate Minority Leader Mitch McConnell (R) is still beatable but that Senate Democrats have to prioritize sitting Senators at this point in the election cycle. "The DSCC action is less about the viability of the race, and probably the recognition that, in tough years the priority — in the House AND the Senate — is protecting the incumbents," said the source. "In other words, defense not offense."

Another Democratic consultant tracking the McConnell-Grimes contest largely agreed, noting that pulling money out of Kentucky means "you can play in Georgia, which is within the margin and the trend lines are going the right way, expand buys in Arkansas, Alaska, North Carolina, Colorado, Iowa and Louisiana, which are all neck and neck, and then gamble on a wildcard like South Dakota."

That same Roll Call story noted that the DSCC had just bought its first advertising time of the election cycle in Georgia where Michelle Nunn (D) remains surprisingly competitive against businessman David Perdue (R). And, last week the DSCC dropped $1 million in South Dakota, a Democratic open seat race where former Gov. Mike Rounds (R) is underperforming and former Republican Sen. Larry Pressler, who is running as an independent, and former congressional candidate Rick Weiland (D) are now within striking distance.

All of the DSCC's moves come as its Republican counterpart -- the National Republican Senatorial Committee --  is spending an additional $7.4 million on ad buys in six statesSouth Dakota, Alaska, Colorado, Georgia, Iowa and New Hampshire. Last week, the NRSC announced it was pulling its TV commitment from Michigan's open seat.

The reality of the Kentucky Senate race is that the electorate is simply locked in, polarized to the point where persuadable voters are non-existent. "McConnell has consistently held a mid-single digit lead which in a race that is so well-litigated there are very few movable voters," said one Democratic operative. "Plus, its Kentucky." (President Obama won just 38 percent in the state in 2012 and his approval numbers there nowadays would be lucky to break 30.)

In short, this was a difficult race from the start that got even more difficult when a) McConnell dispatched a tea party primary opponent with relative ease and b) Obama's numbers in the state never stopped trending downward.  It's uniquely possible that Grimes could lose by only a point or two -- at which point the second guessing of the DSCC's decision would begin in earnest. But, getting Grimes to 48 percent is easy; getting her over 50 percent in an election cycle like this one in a state like Kentucky is a lot less easy. All of the election models had begun to agree on this point; probabilities of a McConnell win ranged from 75 percent to better than 99 percent in the three main models.

With Kentucky now effectively off the map, the Senate playing field is now comprised almost entirely of Democratic -held seats. (Georgia's open seat and Kansas Sen. Pat Roberts are the two exceptions.) If you assume Democratic-held open seats in West Virginia and Montana are gone and that South Dakota remains a long shot, then Democrats need to find a way to win four of these six races: Alaska, Arkansas, Colorado, Iowa, Louisiana and New Hampshire.  If they are able to upset Roberts in Kansas, they need to split those six races to keep the majority.

That's a tall task. How tall? President Obama averaged 45.6 percent of the vote in those six states in 2012 even while he was winning reelection convincingly.