Cara Richardson, USA TODAY
Now that Tuesday's election is over, the fight for the U.S. Senate takes center stage.
Much of the battle for control of the Senate in 2014 will be in open races. West Virginia, Montana and South Dakota are states where Republicans could make gains. But experts say incumbents on both sides of the ticket will be a large part of the story line at the ballot box.
"Six is the magic number, and the majority will be won or lost based on a handful of incumbents," said Nathan Gonzales, an analyst with the non-partisan Rothenberg Political Report.
If Republicans can net six seats, they will gain control of the upper chamber, which they haven't had since 2006. They would have the ability to override any tiebreaking vote by the vice president.
In Kentucky, Senate Minority Leader Mitch McConnell is fighting battles from the right and the left.
The five-term senator faces a primary challenge from businessman Matt Bevin, who has the backing of the Tea Party. If he overcomes that hurdle, McConnell will face an Election Day challenge from Kentucky Secretary of State Alison Lundergan Grimes, 34, a Democrat who won the statewide office in 2011 with 60% of the vote.
The non-partisan Cook Political Report rates Kentucky a tossup in the general election, and analyst Jennifer Duffy says McConnell is sitting in "Republicans' most endangered seat."
"There will be a lot of national attention on this race," she said. "Before McConnell even gets to the general election, he's got a Tea Party primary to deal with."
Lundergan Grimes, the daughter of a former Kentucky state Democratic Party chairman, has a tough fight ahead of her. Kentucky leans conservative: In 2010, the election of Tea Party firebrand Rand Paul cemented the Tea Party sea change. In 2012, Mitt Romney won the state with 60% of the vote.
"(McConnell's) saving grace may be that he gets to run for re-election in Kentucky, a place where President Obama has never been popular," Gonzales said.
Second-term incumbent Sen. Lindsey Graham of South Carolina also faces primary challengers; however, the seat would probably remain in Republican control.
A number of Democratic incumbents are also vulnerable in 2014. Mark Begich of Alaska, Mark Pryor of Arkansas and Mary Landrieu of Louisiana are top GOP targets. North Carolina's Kay Hagan also has a fight ahead of her. All four represent states carried by Romney in 2012.
Despite Arkansas' history as a Democratic stalwart, Pryor is the lone Democrat in the state's congressional delegation. He faces a challenge from freshman U.S. Rep. Tom Cotton, 36, an Iraq and Afghanistan veteran.
"This is the one place Republicans actually agree with each other (on a candidate): There is no establishment-Tea Party fight," Duffy said. "Tom Cotton is a consensus candidate."
Begich is vulnerable, but the GOP race is still shaping up and looks to be at least a three-way primary. Joe Miller, who gained attention in 2010 by beating Sen. Lisa Murkowski in a primary, is in the race as is Lt. Gov. Mead Treadwell. Dan Sullivan, head of the state's natural resources department, also is running.
"As long as it's not Joe Miller who emerges to challenge Begich, I think it will be one of the top races in the country," Gonzales said, noting that the Tea Party support that was there for Miller in 2010 seems to have waned.
Pryor and Landrieu both voted for the health care law, which will be tough for them to defend in their increasingly conservative states.
"Landrieu is going to have to defend a lot of votes, not the least of which is health care," Duffy said. "And in Arkansas, the only thing less popular there than the health law? President Obama."
Swing-state first-term Democrat Hagan will also have to defend herself on health care. Republicans know she's vulnerable and have attacked her as "the deciding vote" on Obamacare, according to a September memo from the National Republican Senatorial Committee. She defeated incumbent Sen. Elizabeth Dole in 2008. Obama carried North Carolina in 2008 but not in 2012.
For Democrats,t there are few seats to pick up to offset any losses.
"While Democrats have nowhere really to go to expand their field, Republicans do -- and the path to the Republican majority is very narrow," Duffy said.