According to the latest statistics compiled by the Minneapolis Star Tribune, Norm Coleman's campaign has thus far challenged 240 ballots in Minnesota's recount process, whereas the Franken campaign has challenged 172 ballots, a 68-ballot gap. If the rate of challenges holds steady as the rest of the state's ballots are re-counted, that would mean the Coleman campaign would send about 1,050 ballots to the state's canvassing board as compared with roughly 750 from Franken.
'Challenged' ballots can fall into a number of different categories. One common category is when a vote that had previously been determined to be legal is disputed by one of the campaigns. In such cases, the vote is deducted from the opposing candidate's total. All challenged ballots will then be reviewed by the state's five-person canvassing board in December.
Minnesota Public Radio has examples of many challenged ballots. As you can see, the reason for the challenges run the gamut from the obvious to the frivolous. In some cases, ballots may also be challenged by both campaigns.
Local news accounts contain numerous examples of precinct-level elections officials attempting to dismiss frivolous challenges before they are forwarded to the canvassing board, although it is less than clear what legal standing they have to do so. In practice, the prevailing standard seems to be 'Minnesota nice', with most disputes being resolved amicably and by consensus.
Nevertheless, given the ever-increasing gap in the number of challenges, one wonders whether the Coleman campaign has instructed its precinct-level representatives to challenge ballots aggressively, even if such challenges are almost certain to be rejected by the canvassing board. Their incentive to do so might be as follows: whichever candidate leads at the end of the first phase of the recount process -- before the canvassing board reviews any challenged ballots -- will be able to claim some sort of moral highground. By being able to deduct ballots from their opponent's total essentially at will, the campaigns increase the likelihood that they will in fact lead at the end of the first-phase count with each additional ballot that they challenge.
The incentives may be particularly powerful for the Coleman campaign, because Minnesota has a Democratic Secretary of State (although the five-person canvassing board he appointed appears to be divided roughly evenly across the political spectrum). If Coleman leads at the end of both the initial count (as he did) and the first phase of the recount process, but falls behind Franken after the canvassing board completes his review of the challenged ballots, he will probably attempt to complain later that Democratically-appointed canvassing board had "overturned the will of the people". This might give him greater leverage to demand a second recount or even a re-vote in the event that he falls behind. It might also plausibly affect the mindset of the canvassing board when reviewing the challenged ballots.
To make clear, this behavior is perfectly above-board and 100 percent within Coleman's rights. It is also 100 percent smart. But the Franken campaign should make sure it understands the incentives here, and perhaps do away with some of that Minnesota nice.