Making appeals based on race is not new in politics. It can be subtle, like the posters of President Obama sitting in a barber's chair that hung in black barbershops in 2008. Or it can be overt and bordering on offensive, like the lynching images left on the car windows of black churchgoers in North Carolina. (For their part, conservatives in the state are running ads that ask this question: “Does Kay Hagan care that 1 out of 3 babies aborted in America are black?”)

As the push to get black voters to the polls comes down to the wire in the midterms, Democrats and progressive groups are using such images to engage black voters. Ferguson, Trayvon Martin and kids in bulletproof vests have all shown up in fliers, radio ads and Web videos. The goal behind the appeals — whether subtle or overt — is the same: to spark some sort of emotional connection, either positive or negative, in a voter.

Take, for example, the barbershop posters, which said to black voters: "Obama is one of us."

The Ferguson images, circulated by Georgia Democrats, essentially say to black voters that Republicans are definitely not.

So, how is it that the appeals to black voters have gone from pictures of a smiling Obama in barber's smock in 2008 to images of black kids and police brutality in 2014?

In a New York Times article about the tactics, former Republican National Committee chairman Michael Steele, who is black, said:

They have been playing on this nerve in the black community that if you even so much as look at a Republican, churches will start to burn, your civil rights will be taken away and young black men like Trayvon Martin will die. The reality of it is, the Democrats realize that their most loyal constituency is not as loyal as they once were.

Steele's suggestions aside, there's little proof that African Americans, two years after voting in record numbers for Democrats, have had a change of heart and are poised to vote Republican.

There has been a more notable shift in how African Americans feel about race, however. And the shift means that it's now easier to "play on the nerves" of black voters. Consider this snapshot on race relations over the past seven years, and particularly the changes between 2009 and 2014:

There is clearly an Obama bounce in these numbers. In 2009, the year he was inaugurated, African Americans were especially high on their relationships with whites. Five years later, that's changed markedly.

One common Republican theme in 2012 was Obama as divider, slicing and dicing Americans into groups. Sen. Marco Rubio (R-Fla.), speaking in South Carolina, captured it best when he said that the country had "not seen such divisive figure in modern American history as we have over the last three and a half years.” Under that logic, fault  for the widened racial gap between whites and blacks begins and ends at the White House.

America has been engaged in one long ongoing national conversation about race, and Obama's ascendance is one major inflection point — though not the only one. The subtext of his first national campaign victory in Iowa's caucuses was that a black man could win white Iowa. When Obama said in his 2008 presidential victory speech, "we are one people," he was talking about race as much as any other division. He was, in his own formulation, the repairer of the breach.

But once in office, there was a clear racial backlash. Only a black president with a Kenyan father could spark such widely held birth certificate suspicions. Only a black president could spark cartoonists, washed-up rockers and random elected officials to make watermelon jokes, talk about a "mongrel" background and use racial epithets. Only a black attorney general (Eric Holder) could wonder aloud about why his treatment at a congressional hearing seemed so different and disrespectful — and get nods of recognition from a black audience.

This is the backdrop against which these overt racial appeals are being made. In the minds of many African American voters, Republicans have a race problem. And Obama's presidency has magnified it to a degree not seen over the last decades.

The efforts to emphasize Ferguson and lynching exploit that perception — one that Republicans will likely have to work for years to overcome.