Senate Republican leader Mitch McConnell of Kentucky holds a news conference on the day after the GOP gained enough seats to control the Senate in next year's Congress and make McConnell majority leader. (J. Scott Applewhite/AP)

Congratulations, Republicans! You won the Senate majority! Now, can you hold on to it for more than two years?

Looking at the 2016 Senate map, there’s reason for doubt. Republicans will have to defend 24 seats, compared with 10 for Democrats. And the raw numbers don’t even tell the whole story. Seven seats held by Republicans — Florida, Illinois, Iowa, New Hampshire, Ohio, Pennsylvania and Wisconsin — were carried by President Obama in 2008 and 2012. And there is chatter about potential Republican retirements in Arizona and Iowa. If either John McCain or Chuck Grassley decided to call it a career, each of those races would be major Democratic targets.

On the other side of the coin, Republican takeover opportunities are few and far between. By far, the most endangered Democrat is Senate Majority Leader Harry Reid, who survived in 2010 but could face Nevada Gov. Brian Sandoval (R), who won a second term Tuesday with more than 70 percent of the vote. Reid has said he will run again, although his demotion from majority leader to minority leader might make him rethink those plans. The only other Democrat who starts the 2016 cycle in serious jeopardy is freshman Michael Bennet (Colo.), who, like Reid, was a surprise winner in 2010. The convincing win by Cory Gardner (R) over Sen. Mark Udall (D) on Tuesday in the Rocky Mountain State will undoubtedly energize Republicans, though it’s less clear what the GOP bench looks like in a race against Bennet.

Outside of those two seats, there’s almost no vulnerability on the Democratic side. Even if Sen. Barbara Boxer (Calif.) or Barbara Mikulski (Md.) decide not to run again, both sit in very, very Democratic states — particularly at the federal level.

To win back the Senate majority in two years, Democrats will probably need to net four (if they hold the White House in 2016) or five (if they don’t) seats. Republicans control 52 Senate seats in the 114th Congress, but Sen. Mark Begich (D) is behind by 8,000 votes in Alaska and is likely to lose, and chances for Sen. Mary Landrieu (D) don’t look great in Louisiana’s Dec. 6 runoff.

Gaining five seats is not out of the question for Democrats — though it might be a bit of a stretch — given the Senate map of 2016. Of the 10 most vulnerable seats listed below, Republicans hold eight. The No. 1 race is the most likely to flip party control in 2016.

10. Kentucky (Republican-controlled): As Tuesday’s election showed, Kentucky isn’t exactly fertile ground for Democrats. But something interesting happened even as Mitch McConnell walloped Alison Lundergan Grimes: Democrats held on to their majority in the state House. That means Sen. Rand Paul (R-Ky.) can’t count on changing state law to be able to run for president and Senate at the same time. Hence, a possible open seat.

9. Florida (R): Sen. Marco Rubio (R) has suggested that he won’t run for both president and reelection to the Senate in 2016. If he pursues the former and isn’t on the Senate ballot, this becomes an open-seat race in a true swing state in a presidential year — in other words, a good opportunity for Democrats. If Rubio passes on a White House bid or drops out with enough time to mount a Senate bid, Republicans would probably feel better about holding this seat.

8. Ohio (R): Sen. Rob Portman is one of several Republican members of Congress who have been mentioned (or mentioned themselves) as possible White House contenders. So, this could end up being an open seat. If Portman decides to run for reelection, his deep connections to donors through his work as National Republican Senatorial Committee vice chairman should ensure that he will be a financial behemoth. Portman is not terribly polarizing, and there is no obvious Democratic recruit waiting in the wings.

7. New Hampshire (R): The Granite State was one of the few bright spots for Democrats nationally as Sen. Jeanne Shaheen (D) beat back a challenge from Scott Brown. It could be a Senate battleground again in two years if Gov. Maggie Hassan (D), who won reelection Tuesday with 53 percent of the vote, decides to take on freshman Sen. Kelly Ayotte (R). There is also considerable chatter among conservative activists about a primary challenge to Ayotte, though it remains to be seen whether a serious one might materialize. And, just to make things more complicated, Ayotte is likely to be in the vice presidential mix no matter who wins the Republican presidential nomination.

6. North Carolina (R): The GOP picked off a seat here Tuesday. It’s safe to assume, however, that if the environment wasn’t so good for the GOP, Kay Hagan would still be a senator come January. Her colleague, Sen. Richard Burr (R) is up for reelection in 2016, and even if he doesn’t retire — he has raised very little money the past two years, which is usually a precursor to retirement — he is likely to find himself targeted.

5. Colorado (Democrat ic-controlled): Bennet probably doesn’t want to think about 2016 yet. He just finished a stint as chairman of the Democratic Senatorial Campaign Committee, during which his party lost the Senate majority and he became the first chairman in more than four decades to lose a home-state colleague in the process. But Bennet won by the narrowest of margins in 2010 and probably would have lost had Ken Buck, the Republican candidate, not said some unhelpful things.

4. Pennsylvania (R): 2010 was about as good a year as a Republican could hope for in Pennsylvania. And Sen. Pat Toomey (R) still won with only 51 percent of the vote. In a presidential year, Toomey’s challenge will be even more serious. Republicans haven’t carried the Keystone State at the presidential level since 1988. One thing working in Toomey’s favor: a relatively weak Democratic bench. State Attorney General Kathleen Kane apparently has no interest in running for the Senate. The only person actively looking at a bid is former congressman Joe Sestak, who lost to Toomey in 2010.

3. Illinois (R): The first big question that needs to get answered in this race is whether Sen. Mark Kirk (R) will run again. Kirk, who suffered a severe stroke in early 2012, has insisted that he plans to seek a second term, but even some Republicans are taking a wait-and-see approach. Democratic speculation — matter what Kirk does — will center on state Attorney General Lisa Madigan, but she seems a much more likely 2018 challenger to Gov.-elect Bruce Rauner (R). Assuming Madigan is a no-go, look for Rep. Tammy Duckworth to be at the top of Democratic wish lists.

2. Nevada (D): Reid will soon no longer be majority leader. The question is whether he wants to be minority leader and whether he sticks around. He’s got bad approval numbers and is staring at a potential matchup with Sandoval. Tuesday’s election was actually pretty big here. Not only did Sandoval cruise to reelection with 71 percent of the vote — 71 percent! — the GOP also cruised in the lieutenant governor’s race, a huge proxy war that Reid badly wanted to win. That means Sandoval can run in 2016 without worrying about the governor’s seat going to a Democrat.

1. Wisconsin (R): Sen. Ron Johnson starts the 2016 election cycle as the most vulnerable senator on the map. He’s undefined in the eyes of many, and he’s running in a state that has gone Democratic in seven straight presidential elections. To boot, there are rumors that Democrat Russ Feingold, whom Johnson unseated in 2010, may run.