These 10 races could decide control of the U.S. Senate

Control of the U.S. Senate and the political agenda in Washington are at stake in the Nov. 4 elections. The outcome will determine whether Republicans control both chambers of Congress, which would give them power to thwart the president's policy initiatives and set the stage for the 2016 presidential election. A look at the 10 tossup races that will be decisive:

The incumbent has run a top-notch campaign, but he pulled down a controversial crime attack ad this month that may have lingering effects. Obama lost big here in 2012.

Democrat Sen. Mark Begich

Why he'll win: He portrayed his opponent as an "East Coast outsider" who lived in Maryland while claiming to be an Alaskan.

Republican Dan Sullivan

Why he'll win: He has GOP establishment support, plenty of cash and red-state credentials as former attorney general and natural resources director.

Talking point: Sullivan once worked for Sarah Palin and former Secretary of State Condoleezza Rice.

Obama's unpopularity is a drag on the incumbent, who is a top national GOP target, but Pryor is popular; he didn't even have a Republican opponent in 2008.

Democrat Sen. Mark Pryor

Why he'll win: He invoked his closeness with former President Bill Clinton, who was once Arkansas' governor and is still beloved.

Republican Rep. Tom Cotton

Why he'll win: Increasing Republican dominance in the Deep South also has taken root in Arkansas, and Obama is unpopular here.

COLORADO

In a sign of GOP confidence, the challenger abandoned a safe House seat to run. This could become the most expensive Senate contest in the state's history.

Democrat Sen. Mark Udall

Why he'll win: Democrats here know how to buck Republican waves; they got Democratic Sen. Michael Bennet elected in 2010.

Republican Rep. Cory Gardner

Talking point: Gardner was among Americans whose health insurance was canceled under Obama's Affordable Care Act.

GEORGIA

Once a reliably Democratic state, things changed in Georgia in 2002, when rural white voters evicted a Democratic governor and senator. In 2004, the GOP won the House.

Democrat Michelle Nunn

Why she'll win: Her father, former Sen. Sam Nunn, is a beloved figure in the state, and shifting demographics might favor Democrats.

Why he'll win: This is still a Republican state. He's strong in rural areas.

Talking point: Nunn once worked for a Republican, heading George H.W. Bush's Points of Light Foundation.

IOWA

Obama's campaign took flight here in 2008 and he carried the state twice, but his average approval rating this year has averaged 38 percent — 5 points lower than his national average.

Democrat Rep. Bruce Braley

Republican state Sen. Joni Ernst

Why she'll win: Iowans' confidence in the economy is low and Democrats get the blame.

Talking point: Ernst's campaign ad touting her experience castrating hogs went viral.

KANSAS

This has been a chaotic campaign. Democratic challenger Chad Taylor withdrew this month without explanation, but his name will remain on the ballot.

Why he'll win: He's got plenty of cash and his candidacy is the only destination for frustrated Democrats — and Republicans.

Republican Sen. Pat Roberts

Why he'll win: He successfully paints his challenger as a Democrat in disguise and Republican voters stick with him.

Talking point: Milton Wolf, who lost to Roberts in the primary, is a distant relative of President Obama.

This year's most expensive and bitter race. The Senate minority leader is very unpopular; his challenger is a stellar fundraiser who is giving her party hope.

Why she'll win: She secures enough votes from the longstanding Democratic base in coal country.

Republican Sen. Mitch McConnell

Why he'll win: Having your guy running the show in a Republican-controlled Senate is pretty appealing.

Talking point: McConnell and likely 2016 presidential candidate Rand Paul's once-testy relationship has become a close partnership.

LOUISIANA

Democrat Sen. Mary Landrieu

Why she'll win: She's a survivor, edging out challengers in each of her three previous races, and she distances herself from Obama's energy policies.

Why he'll win: He's the front-runner among Republicans and a flap over where Landrieu actually resides hurts her chances.

Talking point: This is one of the few Senate races where the Affordable Care Act is a key issue.

MICHIGAN

Democrat Rep. Gary Peters

Why he'll win: He represents the Detroit suburbs in Congress and has broad support in the African-American community.

Republican Terri Lynn Land

Why she'll win: She has a financial advantage, and popular Republican Gov. Rick Snyder shares the ticket with her.

Talking point: No Republican has won a U.S. Senate race here since 1994.

Obama won the state in 2008 and lost it in 2012. Outside money helped the challenger overcome Tea Party opposition to win the GOP primary.

Democrat Sen. Kay Hagan

Why she'll win: Obama postponed immigration changes and Democrats still hold an edge in the battle turnout, which could help in 2016, too.

Republican House Speaker Thom Tillis

Why he'll win: He paints Hagan as a "rubber stamp" for Obama initiatives and fends off her attacks on the statehouse he helps run.

Staff and wire reports