With 100 days to go until Election Day, Senate Republicans have plenty of reasons to be optimistic about winning the majority — but they also have grounds for concern.

After coming up short in 2010 and 2012, the GOP is unquestionably well positioned to finish the job this time. Republicans need to match their November 2010 score of six seats to take the majority, and the party has multiple paths to the finish line.

That’s thanks to a successful recruitment push that didn’t conclude until late February, and a playing field naturally tilted in the GOP’s direction — seven Democrat-held seats are in states President Barack Obama lost in 2012, six of those by double digits.

But, as optimistic as Republican operatives are heading into the final stretch, the GOP has reasons to restrain its confidence. With tens of millions of dollars of advertising already spent by outside groups on both sides, just one Democratic incumbent is, at this point, a solid underdog for re-election.

Reasons for Republicans to Be Optimistic

They’ve got a three-seat head start. As things stand today, Republicans are solid favorites to pick up the Democrat-held open seats in South Dakota and West Virginia, and to defeat appointed Sen. John Walsh in Montana — particularly after plagiarism revelations last week. That means they need three more out of a plethora of options including seats in Arkansas, Louisiana, North Carolina, Alaska and Colorado.

And in just the past month, the open seat in Iowa has progressed into a Tossup race, in part because of missteps by Democratic Rep. Bruce Braley. That’s a wide playing field encompassing several states the president lost in 2012, and it’s one that will force well-funded national Democrats to spread their money around to more states.

They’re in a favorable environment. Obama won’t appear on a single ballot in November, but he remains a motivating factor for voters on both sides — especially Republicans. A Pew Research Center survey released last week found Obama with a 44 percent job approval rating overall and lower marks for his handling of specific issues such as the economy and foreign policy.

The poll also found Republicans were both more enthusiastic than in past elections and more likely to vote than Democrats. That matters, particularly in states the president performed poorly in 2012 and where the Affordable Care Act could prove to be a formidable issue. The onus is on Democrats to rally their base.

The GOP survived the primaries. Over the past two months, Republicans dodged nomination bullets in Mississippi, Georgia and Iowa, where Joni Ernst’s primary victory kept the party from going to an unpredictable nominating convention for a tantalizingly vulnerable open seat. Earlier this year, the National Republican Senatorial Committee scored a big victory in Colorado by swapping out Ken Buck, who lost in 2010, for the more potent candidate in Rep. Cory Gardner.

That is a change in fortune for the GOP from recent cycles. In 2012, Rep. Todd Akin’s nomination in Missouri and Sen. Richard G. Lugar’s primary defeat in Indiana directly contributed to a disappointing cycle for Republicans. Rather than win back the Senate, the party actually lost two seats. It faced a similar issue of flawed candidates emerging from primaries in 2010 — but not this year, as Republicans tout a formidable team of candidates.

Reasons for Republicans to Be Concerned

It’s hard to beat incumbents — especially Democrats. Republicans will likely need to defeat at least three Democratic incumbents to pick up six seats, and the party simply has a weak track record of doing that. A grand total of 14 incumbents have been defeated in general elections over the past five election cycles, which includes three straight wave cycles from 2006 to 2010. Of those, just three were Democrats, dating back to then-Senate Minority Leader Tom Daschle of South Dakota in 2004.

Republicans are favored to win the open seats in South Dakota and West Virginia, and they have an even chance in Iowa. But in Michigan, home to the only other Democrat-held open seat, four polls conducted in the past month have found Republican Terri Lynn Land down by significant single-digit margins. So figuring out the calculus to take out sitting senators is imperative.

Democrats are raising a lot of money. While 2014 continues to look like a strong year for Republicans overall, there is no sign of apathy among Democratic donors. The party’s fundraising spigot is on full blast, with the Democratic Senatorial Campaign Committee outraising the NRSC by $25 million through June, and incumbents filing another strong quarter of receipts this month. Senate Majority PAC has also proved to be a force on the airwaves and promises to continue that into the fall.

Candidate money will soon become even more valuable, as the campaigns — which get better airtime rates than outside groups — will represent a greater percentage of the overall media spending. Two of the top Democratic fundraisers are Alison Lundergan Grimes of Kentucky and Michelle Nunn of Georgia, who represent the party’s only two pickup opportunities.

The Republican brand isn’t so hot either. The NBC News/Wall Street Journal poll in June found just 38 percent of voters with at least a somewhat positive view of the Democratic Party. That’s low, except when compared with the Republican Party, which just 29 percent see at least somewhat positively.

Republicans are counting on their recruits from the House — which isn’t exactly popular either — to take down some of the Democrats’ most endangered incumbents. That includes Gardner in Colorado and Reps. Tom Cotton in Arkansas and Bill Cassidy in Louisiana. In 2012, just one of the five House Republicans with legitimate shots at the Senate was elected.

While Republicans say questions over the competence of the president is a more compelling case, Democrats think they win those seats if the races are about the two candidates and their records.

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