How The 'Orman Factor' Muddles The Senate Forecast, And How We've Dealt With That

WASHINGTON -- The recent upheaval in the Kansas Senate race has thrown a small wrench into political observers' efforts to forecast which party will take majority control of the upper chamber of Congress next year.

If independent candidate Greg Orman ousts Sen. Pat Roberts (R-Kan.) on Nov. 4, three outcomes are possible in the overall battle for the U.S. Senate : The Republicans might still have won enough seats to take over. Democrats might retain control. Or an Orman victory could trigger a "little-known third category " -- a stalemate in which the Kansas businessman decides which party holds the majority.

To deal with this possibility, we are making a slight adjustment to the HuffPost Pollster Senate Forecast .

First, some background. Orman is a former Republican who flirted with a run for the U.S. Senate as a Democrat before he "parked himself firmly in the middle" of the political spectrum, as The Washington Post reported . His independent candidacy had already been gaining ground in polls when, on Wednesday, Democratic nominee Chad Taylor abruptly pulled out of the race. On Thursday, the Kansas Secretary of State ruled that Taylor's name must remain on the ballot.

Though new polling hasn't been released since Taylor quit the race, the shake-up leaves incumbent Roberts "the most vulnerable Republican senator in the country," according to The Rothenberg Political Report's Nathan Gonzales .

The problem for election forecasters is that Orman has given a novel answer to the question of which party he would caucus with should he win. "If one party is clearly in the majority," Orman's campaign website says , "he will seek to caucus with the party that was in the majority as that would be in the best interest for the state of Kansas."

More importantly, Orman has been coy about what he might do in the event his caucus choice would determine which party held the majority. "If I get elected, theres a reasonable chance that neither party will have a majority in Washington," Orman told MSNBC's Steve Kornacki . "If that is the case, I'm gonna caucus with whichever party is willing to actually go to Washington and start trying to solve problems as opposed to just pleasing the extremists in their own base."

This ambiguity is a problem for the HuffPost Pollster Senate Forecast and other statistical models attempting to predict the outcome of the greater Senate battle. If either party wins a majority with room to spare, Orman's choice is irrelevant. If Democrats end up with 50 seats or Republicans win 51, Orman can give the majority party one extra vote, but his choice will not decide which party takes control. (Vice President Joe Biden votes with the Democrats to break ties, so Democrats would have a working majority with 50 votes in their caucus.) However, if the Democrats hold 49 seats and the Republicans win 50, Orman will be in a position to determine the majority.

To account for the possibility of Orman breaking a stalemate, we've made slight adjustments to the final stage of our forecast model (we previously described the workings of our poll tracking model and overall Senate forecast in more detail). We still calculate the probability of Republicans taking the majority or Democrats holding the majority using the simulation method described in our earlier stories. Now, however, in the simulations that project an Orman win, our model will usually assign him to the party in the majority.

In the rare scenario in which Orman wins and the chamber is split with 49 Democrats and 50 Republicans, we give Orman a 50 percent chance of caucusing with the Democrats and a 50 percent chance of caucusing with the Republicans. (Thus, the overall probabilities of each party's winning the majority still add to 100 percent.) But we also note the probability of this situation occurring -- we call it "the Orman factor." On the Senate model dashboard , this number appears right below the probabilities for Democratic and Republican majorities.

Other models have also assigned Orman to one side or the other in the case of 49 Democrats and 50 Republicans, but in slightly different ways: Daily Kos similarly assumes there is a 50/50 chance Orman will caucus with each party, but FiveThirtyEight assumes a 75 percent chance he will caucus with the Democrats, and The Upshot assigns him to the Democrats 100 percent of the time.

There are some practical limits to how much a forecast like this can predict. Currently, the Democratic Senate caucus includes two independent senators, Bernie Sanders of Vermont and Angus King of Maine. Neither is up for re-election this year, but theoretically either could make a different caucus decision when the Senate reconvenes next year. For that matter, any senator could opt to switch parties, as Jim Jeffords of Vermont did in 2001 , shifting control of the Senate from the Republicans to the Democrats.

With these adjustments, however, our Senate forecast should best reflect the potential impact of the "Orman factor."