U.S. President Barack Obama steps off Air Force One as he arrives in Tallinn, Estonia, Wednesday, Sept. 3, 2014. (AP Photo/Charles Dharapak)

It's been obvious for a while now that President Obama was going to be a net negative for Democrats trying to hold onto control of the Senate on Nov. 4.  But, just how big a drag he actually is has come into focus over the last few days -- thanks to a slew of polling in some of the most hotly contested races in the country.

Let's start in Kentucky -- where polls by NBC-Marist and CNN-Opinion Research Corporation have been released in the last few days.  Both show Senate Minority Leader Mitch McConnell leading Secretary of State Alison Lundergan Grimes by between four and eight points.  In the NBC poll, 31 percent of voters approve of Obama while 62 percent disapprove. The CNN poll paints an even grimmer picture for Democrats; 29 percent approve of Obama, 64 percent disapprove.

In Arkansas -- where Sen. Mark Pryor (D) is trying to fight off a challenge from Rep. Tom Cotton (R) -- the story is the same.  The NBC-Marist poll puts Obama approval in the state at just 31 percent while CNN has Obama at a similarly miserable 33 percent approval.

And, it's not just in southern states where Obama is making it harder for his party to hold the Senate. An NBC-Marist poll in Colorado -- where Sen. Mark Udall (D) holds a six-point edge over Rep. Cory Gardner --  shows Obama at just 39 percent approval.  In Iowa, a state Obama won twice and where Rep. Bruce Braley (D) and state Sen. Joni Ernst (R) are locked in a tight fight, the president's approval is at just 38 percent, according to a Gallup poll.

But, wait, Democrats argue. Heidi Heitkamp won in North Dakota in 2012 with Obama taking just the 39 percent of the vote. Joe Donnelly won in Indiana as Obama lost by 11 points.

True. But those were races set against the backdrop of a presidential electorate, which, as we know is a) larger and b) favors Democrats, demographically. A midterm electorate, like the one Pryor, Grimes and Udall are running in tends to favor traditional Republican constituencies aka older, whiter voters.

It's also worth noting that while Obama didn't exactly light the world on fire in Arkansas (37 percent) or Kentucky (38 percent) in 2012, he has grown even less popular in both of those states -- not to mention places he won in 2012 like Colorado and Iowa -- over the intervening two years.

The problem in all of this for the Pryors and Grimes of the world -- not to mention Mary Landrieu in Louisiana and Mark Begich in Alaska -- is that their path to victory involves overperforming the most well-known politician in their party by 15+ points with an electorate that is already tilting against them.

Yes, Senate Democratic strategists have long known that Obama wasn't going to be a huge positive -- or a positive at all -- in many of their key races and, with that in mind, have worked to localize campaigns (Alaska is an example of that strategy has worked well to date) and to build individualized turnout operations to ensure they bring out as much of the Democratic base as possible. But, Obama, at least at the moment, looks to be be a bigger drag on Democratic candidates in races Democrats must win than anyone in the party likely believed he would be even six months ago.

In short: Alison Lundergan Grimes could win -- not would win but could win -- if President Obama's approval ratings in Kentucky were at, say 38 percent.  At 28 percent, it's almost impossible to see how she ends up on top. The hardest thing about that reality for Senate Democrats is that there isn't much they can do about it; they simply need to wait and hope that Obama's numbers in 57 days time don't look like they do today. If his numbers stay the same or erode even further, Democrats' chances of holding the Senate disappear.