The big news in progressive circles today is that Democrat Bill Halter, the Lieutenant Governor of Arkansas, jumped into the primary against Blanche Lincoln for the US Senate.

Arkansas Lt. Gov. Bill Halter says he is seeking the Democratic nomination to challenge U.S. Sen. Blanche Lincoln this fall.

Halter’s spokesman provided a statement Monday in which Halter said he would file papers for the Senate this week. Halter is the only Democrat to formally announce a challenge to Lincoln as she seeks a third term.

Lincoln faces a tough re-election fight, with eight Republicans already announcing interest in the seat. Groups on the left have criticized her stances on labor, health care and air pollution regulations.

Halter jumped in pretty late in the game. The primary takes place on May 18, a little less than three months from now.

Halter is running with the support of multiple progressive groups (including, full disclosure, the PAC connected to this website), and perhaps organized labor. Presumably, this could help him in a Democratic primary.

However, there’s one key difference here. Arkansas has essentially an open primary format. The key information from the Secretary of State’s website reads:

In a primary election, you must state the party primary in which you wish to vote. If you do not wish to cast a party ballot, you may choose to vote only in the non-partisan races (which may include judicial contests, tax increases and other local issues).

In a primary election, you are allowed to vote only one party’s ballot or the non-partisan judicial ballot. The election official records which party’s ballot you choose.

Max Brantley, a reporter for the Arkansas Times, notes that almost nobody, save for literally a few hundred folks, even registers for a political party in Arkansas. And that registration has no impact on what party they vote for. So really, any registered voter can place a vote in the May 18 primary between Lincoln and Halter.

Now, Halter has been elected statewide, he’s not a fringe candidate, and so the extent to which this hurts him is questionable. However, he indicated in his announcement speech (see the video) that he will run a populist campaign, attacking Lincoln for her unreliability as a Democratic vote in the Senate. So presumably, Republicans who like Lincoln for those reasons could cross over and vote for her in the primary. Now, Halter also cited Lincoln’s support of the bank bailout, which doesn’t go over well with the tea party crowd. A populist campaign could potentially upset those carefully drawn partisan battle lines.

I asked Brantley if there had ever been the experience of a candidate or party “picking the opponent” – in other words, trying to encourage voters to cross over and choose the weaker of two candidates in the opposite primary to boost their candidate’s prospects in a general election. He related a story from about 20 years ago:

Yes. The most famous was in 1990 when Bill Clinton was on the ballot. In the Repub primary, Congressman Tommy Robinson, a wildman former Dem thought to have great strength among the yahoos, faced Sheffield Nelson, oil&gas tycoon. Because robinson was viewed as more formidable — and crazy as shit — and because Clinton had no meaningful opposition, Dems encouraged a crossover to vote for Nelson. The folklore is that the crossover was decisive. I’ve never fully adopted that view, though there’s no doubt there was some crossover of some size, particularly in Pulaski County. To my knowledge, nobody attempted to quantify it by a study of voter records. It would have had to have been done by hand.

The difference here is that the Republican AND Democratic primaries are now contested. There are, at last count, eight Republicans running for the Senate nomination. Rep. John Boozman, Arkansas’ only federally elected official, just announced for the seat, and he may be able to chase a lot of these candidates out. But so far, candidates like State Sen. Gilbert Baker have insisted that they’re staying in the Senate race. So I would view the possibility of Boozman running unopposed for the May 18 primary as remote. Brantley further says that “nobody on either side can throw a vote away,” so crossover voting will not happen to any major degree.

Halter has already raised close to $90,000, at last count, on ActBlue.