Most Americans will focus on election results in Ohio and Florida to see who rides those states’ Electoral College votes into the White House. But the winner of the presidential race will not automatically control the 2013 legislative agenda. Congress still matters. The battle for control of the U.S. Senate is vitally important and just as hard-fought as the top-of-the-ticket contest.

Currently, a caucus of 51 Democrats and two liberal Independents rule the upper chamber. Since the Vice President can cast tie-breaking votes in the Senate, Republicans would have to pick up three seats to gain a working majority in a Romney-Ryan Administration and four seats to gain control of the gavel under a second term for President Obama.

A few months ago, Republicans looked to have a great chance to retake the Senate. Thirty-three seats are up for election, and 23 of them are occupied by members who caucus with the Democrats. But as campaign season winds down, the number of seats still “in play” has shrunk dramatically.

A dozen seats are considered “safe” for the incumbent party. Seven of these--California, Maryland, New York,Vermont, Delaware, Minnesota and Rhode Island—are safe for Democrats. Five—Mississippi, Wyoming,Tennessee, Utah and Texas—are safe for the GOP.

Democrats have significant leads in six other races—in Hawaii, Michigan, New Jersey, New Mexico, Washington, and West Virginia—and are likely to hold those seats. And Florida and Pennsylvania are leaning Democratic (with Bill Nelson and Bob Casey, respectively) as well.

Meanwhile, both sides are expected to lose a seat. Independent Angus King looks to replace retiring Senator Olympia Snowe (R-Maine) and caucus with the Democrats. Republican Deb Fischer holds a narrowing lead over former Democratic Senator and Governor Bob Kerrey in her bid to supplant retiring Nebraska Senator Ben Nelson.

That leaves 11 seats–four occupied by Republicans and seven by Democrats—which Real Clear Politics classifies as toss-up races.

Here’s the situation in the battle for Republican-held seats:

· In Arizona, Rep. Jeff Flake (R) faces off against Richard Carmona, the former Surgeon General of the U.S. Flake has a polling lead, according to Rasmussen.

· In the race to replace Sen. Lugar (R-Ind.), conservative Richard Mourdock is battling with three term Democratic Rep. Joe Donnely. Romney is expected to win this state by over 10 percentage points, yet polling shows the Senate race close, with Mourdock support softening in the last week.

· In Massachusetts, incumbent Republican Scott Brown’s trails the Democratic challenger, Elizabeth Warren. Brown won his Senate seat in a special election. This time he’s running in a general election, with President Obama at the top of the ticket. That makes for tough going in this Democratic stronghold.

· In Nevada, incumbent Sen. Dean Heller is struggling to fend off Democratic Rep. Shelley Berkley.

Meanwhile, the Democrats are playing defense on seven nail biters:

· Montana—A new Rasmussen poll has Sen. Jon Tester (D) and Rep. Denny Rehberg (R) within the margin of error. Romney is expected to win Montana big.

· North Dakota—Rep. Rick Berg (R) seems to be gaining steam, with a very good chance of defeating Heidi Heitekamp in the race to replace Democrat Kent Conrad.

· Connecticut—Republican Linda McMahon trails Rep. Chris Murphy (D) in the contest to replace retiring Independent Joe Lieberman.

· Wisconsin—Moderate Republican Tommy Thompson, a former governor, faces liberal Democratic Rep. Tammy Baldwin for Sen. Herb Kohl’s seat. The state is divided evenly between the parties, yet has gone Republican in two recent statewide elections—Governor Scott Walker and U.S. Senator Ron Johnson

· Virginia—A presidential swing state, the Senate race here features former Republican Sen. George Allen against former Democratic Governor Tim Kaine.

· Ohio—Sen. Sherrod Brown (D-Ohio) retains a polling lead against Josh Mandel.

· Missouri—Sen. Claire McCaskill leads Rep. Todd Akin. In the wake of controversial remarks about rape and conception, Akin was abandoned by national Republican leaders in a race that may determine whether Sen. Mitch McConnell (R-Ky.) or Sen. Harry Reid (D-NV) holds the gavel in the next Congress.

My take? A big night for either Obama or Romney will dramatically impact the 11 Senate toss-ups. If Romney romps, most of the seven Democratic-held toss-up seats could flip. (Montana and North Dakota may flip, even with an Obama victory.) Ohio, Missouri and Connecticut seem to be the most difficult contests for Republicans. McMahon will have a tough time, even with a Romney triumph. The bottom line: A good night for Republicans would get them to 51 seats.

Best case scenario for Democrats hinges on a big win for Obama. Under that scenario, they hold all their endangered seats (with Montana still being difficult) and pick up maybe two of the GOP-held cliff hangers. Hence, a good night for Democrats would net a one seat pick-up, giving them 54 seats.

Election night isn’t just about who gets to sit in the Oval Office. Who rules the Senate will go a long way toward determining which policies ripen and which wither on the vine throughout the next session of Congress.