It's a rich irony that on the 50th anniversary of the Freedom Riders risking life and limb in Mississippi to help African-Americans register to vote, black Democrats may decide which Republican wins Tuesday's runoff for the GOP Senate nomination.

Then again, maybe they won't. A big unknown on the morning of the election is just how many African-American Democrats might actually visit polling places across party lines to vote for Sen. Thad Cochran, age 76, who's been in the Senate for 35 years, in his contest against Chris McDaniel, 41, his Tea Party-backed challenger.

The Real Clear Politics average of publicly available polls gives McDaniel, a state senator and former talk-radio host, a roughly 6-point lead over Cochran, 49 percent to 43.3 percent. It will take 51 percent of the vote for either man to win the nomination. In the June 3 primary itself, neither man attained the 50 percent that would have averted the runoff, though they came close: McDaniel had 49.5 percent, Cochran 49 percent.

This is where black Democrats could be a factor in the racially polarized politics of Mississippi, where blacks make up about 36 percent of the electorate.

Mississippi law allows Democrats to vote in the Republican runoff if they didn't vote in the June 3 Democratic primary, and if they plan to support the Republican candidate in the general election. The second part of that law is very hard to enforce.

Cochran's campaign has made a concerted effort to appeal to blacks. Some of the first people he greets in his most recent ad, for instance, are African-Americans.

This strategy may seem born of desperation on Cochran's part, but it's also logical. Cochran may be right of the political center, but he's certainly closer to that center than McDaniel, who argues for a much smaller government and significantly lower spending and taxes. (Cochran has a 78.9 percent lifetime rating from the American Conservative Union.)

Cochran serves on the Senate Appropriations Committee, an assignment important to a state with some dubious distinctions: the state budget with the largest percentage of revenue coming from the federal government; and relatively high poverty rates for whites and blacks alike. Cochran, for instance, supports the $1.5 billion in federal funding the state gets for education. McDaniel opposes it.

There's a risk to Cochran's outreach to black voters, however. It could result in a backlash that prompts more Republicans to come to the polls for McDaniel.

Some blacks are responding to Cochran's entreaties. An open letter from a local African-American politician, who quoted Martin Luther King Jr., urged Democrats (that is, blacks) to "VOTE YOUR BEST INTERESTS. VOTE COCHRAN!"

McDaniel's conservative supporters aren't taking this lightly. They intend to deploy poll watchers. "Mississippi has total transparency in the conduct of elections," wrote J. Christian Adams in a PJ Media post. "Observers are permitted to observe the process to ensure that Mississippi election laws are followed."

Critics of the conservative poll-watching effort claim it's reminiscent of 20th century efforts to suppress the black vote in the South. A headline on a post on Rick Hasen's Election Law Blog expressed the concern: "Conservative 'Election Observers' in Mississippi May Be Meant to Intimidate Democratic Voters in Cochran-McDaniel Race."

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