The debate continues about whether Republicans can wrest control of the Senate from the Democrats on Election Day and the reality is this: there are currently 12 top battleground Senate states and a net swing of 4 seats would put the GOP back in charge of the Senate. (Just three will swing it if Mitt Romney wins the White House because a Vice President Paul Ryan would break 50-50 ties in the chamber).
The top races that will decide control are in Massachusetts, Montana, North Dakota, Wisconsin, Virginia, and Connecticut (all of which are currently tossups that could go either way) along with Maine, where an independent may win. A few Senate battlegrounds are currently leaning to one side: two are leaning Democratic (Missouri and Hawaii) and three are leaning Republican (Indiana, Arizona, Nevada).
The current number of competitive races is a little larger than many had expected earlier this year, but that's not unusual for Senate races - voters often pay more attention to the presidential race first and tune in to the Senate late. And things will surely shift again, for the same reasons.
A common theme to note: Many of these contests feature Democrats running in Republican "red" states or Republicans running in a blue one. Because of that, if there is one kind of "swing voter" for the Senate, it is surely the "ticket-splitter" - the person who'll consider voting for a different party for President and Senate.
Top Senate Battlegrounds
Tossups: Massachusetts, Montana, North Dakota, Wisconsin, Virginia, Connecticut, Maine
Lean Rep: Indiana, Arizona, Nevada
Lean Dem: Missouri, Hawaii