[I]t is difficult to view Mr. Brown as much better than even money: he is a Republican in Massachusetts who lost an election by a reasonably clear margin just last month. And if Mr. Brown wins, he could well face another competitive election in November 2014, when Democrats will have more chance to gear up from the race – and when Mr. Patrick will have finished his second term as governor and might be more likely to run for the Senate. One thing is for certain: if Mr. Brown is the senator from Massachusetts in January 2015, he will have earned it, having run for office four times in less than five years.
Harry Enten's gives Brown worse odds:
[Y]ou could argue that Brown's victory in 2010 was a fluke more than anything else. Brown's opponent, Massachusetts Attorney General Martha Coakley, ran arguably the worst campaign the state had ever seen. She refused to do much of anything in the way of retail politics – and bragged about it. Coakley made herself an object of ridicule by stating that Boston Red Sox hero Curt Schilling was a member of the hated New York Yankees.
Brown, by contrast, rode his pickup truck around Massachusetts, winning over voters under the radar, and reversed a 30-point deficit in the closing weeks of the campaign. But it's improbable that Brown would catch such a break again.