Everyone knows that the 2014 electorate will be whiter than the 2012 electorate -- and that that change should favor Republicans.

But, no one -- at least that we've seen -- has done a race-by-race analysis of what that less diverse electorate looks like in the states that will decide the Senate majority this fall.  Until now.

The chart below, created by Republican lobbyist Bruce Mehlman, looks at how much less diverse the 2014 electorate could be than the 2012 electorate in 10 of the most competitive Senate races in the country.

The diversity dropoffs in Kentucky and New Hampshire might seem major but are not all that important electorally speaking because neither state has a terrible diverse electorate. Kentucky is almost 88 percent white while New Hampshire is 94 percent white. Alaska is a bit of its own special case. The state is 67 percent white but more than 14 percent Native American.  Eight percent of people identify as a member of two (or more races.)

North Carolina and Colorado may actually be the most interesting --and, for Democrats, worrisome -- states in Mehlman's chart. In each state the non-white vote dropped by more than 13 percent between the 2012 presidential and 2010 midterm elections. In North Carolina, especially, where non-white votes accounted for almost 31 percent of the electorate in 2012, a similar drop-off in the diversity of the electorate in 2014 could be the difference between winning and losing for Sen. Kay Hagan.

The chart speaks to the fundamental challenge at the heart of Senate Democrats' attempts to hold onto control of the chamber this fall.  They must find ways to approximate -- if not duplicate -- presidential turnout among non-white voters. That's a difficult (and expensive) proposition -- but not an impossible one.

As Mehlman notes, the 2013 governor's race in Virginia -- won by Democrat Terry McAuliffe -- proves it can be done.  In 2012, the Virginia electorate was 70 percent white, 20 percent black and five percent Hispanic. The following year, the Virginia electorate was 72 percent white, 20 percent black and four percent Hispanic.  That's pretty damn close.

Now, a single off-year gubernatorial election is not the same thing as a dozen or so competitive federal races in a midterm election. But, if you are looking for how Democrats keep their majority, it's by keeping the diversity drop-off between 2012 and 2014 smaller than it was between 2012 and 2010.