This week on Political Wire's podcast, we spoke to Jennifer Duffy, senior editor for the Cook Political Report, for a look at how some of the most competitive Senate races are shaping up and how the makeup of the upper chamber of Congress could change after November.

Here are five takeaways:

1. Republicans' chances of taking the Senate are going up. Not only have Republicans managed to expand the playing field by recruiting good candidates to compete for Democratic-held seats in Colorado (Cory Gardner) and Michigan (Terri Lynn Land). The political environment is also taking a bad turn for Democrats, Duffy said. President Obama's approval rating has dropped below 40 percent or even 35 percent in key states. And the specter of the president's signature domestic policy achievement, ObamaCare, could loom over some of the most vulnerable Democrats, Duffy said, even though some of the early problems that plagued the insurance-exchange rollout have been addressed: "Despite Democrats' belief that health-care reform is not going to be an issue, we are not seeing that in any of the data," she said.

2. Some vulnerable Democrats have helped the GOP out with miscues. In North Carolina, incumbent Democratic Sen. Kay Hagan was already going to be vulnerable; she was elected in 2008 in a Democratic wave year, and now the political environment is much different. But recently she added to her problems when she launched her campaign. She stumbled in her responses to reporters' questions about ObamaCare. "I think she’s handled the issue really poorly," Duffy said. "It almost appears like she really doesn’t understand how this bill works." Additionally, Sen. Mark Pryor (D-Ark.) was already facing the challenge of his life from GOP Rep. Tom Cotton in the increasingly red state of Arkansas. Then Pryor hurt himself by accusing Cotton of feeling entitled to the Senate because of his military service. "It really didn’t play well, and it’s not going to play well in a state like Arkansas," she said. Still, Pryor's not too far behind Cotton in the polls and still has time to come back.

3. Republicans still could hurt themselves by nominating extreme candidates in some states, including in — believe it or not — Mississippi. So far the Republican establishment hasn't had as much of a "Tea Party problem" as it did in previous cycles. Sen. John Cornyn (R-Texas) easily fended off a challenge from GOP Rep. Steve Stockman, Senate Minority Leader Mitch McConnell (R-Ky.) is favored over Tea Party challenger Matt Bevin, and Joe Miller's return in Alaska hasn't gained steam. But in Georgia, multiple GOP primary candidates are trying to outflank one another on the right. Nominating a very conservative candidate like Rep. Paul Broun could hurt Republicans in this red-tilting state, especially against presumptive Democratic nominee Michelle Nunn, who has run a very good campaign, Duffy said. A similar problem may happen in North Carolina, stymieing GOP efforts to unseat the incumbent Democrat, Hagan. And the deeply red state of Mississippi could actually be competitive if state Sen. Chris McDaniel (R), a Tea Party-aligned candidate, defeats incumbent Sen. Thad Cochran (R-Miss.) in the Republican primary, Duffy said; Democrats have a legitimate candidate there in former Rep. Travis Childers.

4. Nightmare scenario: We may not know who controls the Senate until early 2015. That's because Senate races in two key states — Georgia and Louisiana — could enter runoffs, which wouldn't happen until well after Election Day in November. The general election in Louisiana is actually a primary featuring all candidates from all parties. If no one wins a majority, the race enters a runoff, which would occur in December. Sen. Mary Landrieu (D-La.), who is facing Rep. Bill Cassidy (R-La.), went into a runoff in two of her previous three re-election bids, Duffy noted. And in Georgia, if nobody wins a majority on Election Day, the top two candidates would enter a runoff in early January. It actually happened in 2008, when retiring Sen. Saxby Chambliss didn't initially get a majority against Democratic opponent Jim Martin and the other candidates.

5. Republicans could win anywhere from three seats to six, the latter being the bare minimum to win the majority. That means that a GOP Senate takeover is far from guaranteed, but it's "definitely in the realm of possibility," Duffy said. But she also said it was too early to make a more definitive prediction: "I want to see the outcome of some of these primaries." As was the case in 2010 and 2012, Republicans could still grasp some defeats from the jaws of victory.

Listen to the whole interview here:

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