Labor Day is the unofficial start of the fall campaign season, so it's a good time to assess the GOP's chances of winning the U.S. Senate.
Republicans have two advantages. Many Senate races are in red-leaning states, and the GOP has put its A-Team on the field. In every primary the more electable Republican won the nomination, and that's likely to hold true in New Hampshire on Sept. 9 when Scott Brown is heavily favored.
The GOP candidates also survived Democratic attempts to essentially disqualify them with a summer bombardment of negative television ads. Some GOP hopefuls have been dinged—but the only candidate to implode was a Democrat, Montana's John Walsh, whose campaign collapsed after it was revealed that he plagiarized his Army War College master's thesis. Mr. Walsh withdrew and Democrats chose an eccentric left-wing state legislator to replace him.
But with no positive agenda to run on, Democrats will step up their efforts to portray the GOP as engaged in a "war on women," appeal to class warfare and paint Republicans as extremists. Arkansas Sen. Mark Pryor has carried this last theme to a laughable extreme, claiming that Republican Rep. Tom Cotton opposed preparing against an Ebola virus outbreak. Such overreach invites ridicule.
In the 67 days before the election, it's vital that GOP candidates give a sense of their governing priorities—even as they criticize their opponents and President Obama. This is especially true in races against incumbents.
To regain Senate control, Republicans must defeat at least three incumbents, something they haven't done since 1980 when they defeated 12. The most incumbents Republicans have knocked off since then are two each in 1994 and 2010.
Voters will replace Democratic incumbents when they are convinced they are too closely allied with Mr. Obama, and when the Republican alternative represents constructive change. Republicans should resist the temptation to focus exclusively on the former while neglecting the latter.
Mr. Obama remains something of a wild card. His profile has receded this summer as international crises, private fundraisers and his vacation put him largely out-of-sight, out-of-mind. But he will put himself back at center stage this fall, believing that his involvement is essential to raise money and rally the Democratic base, especially blacks and young women.
Events will also put Mr. Obama front and center. Congress must soon approve a continuing resolution to fund the federal government. Republicans favor longer-term funding while Democrats want a shorter duration. On health care, while the administration has avoided another punishing round of policy cancellations by delaying provisions of the Affordable Care Act, it can't stop ObamaCare premium increases that will hit in the next two months.
As Mr. Obama weighs another imperial executive action, this time on immigration, it appears his calculus is that by granting legal status to millions of illegal immigrants, he will help Democrats cement the long-term loyalty of Hispanic voters while giving Red State Democrats an opportunity to appear independent by disagreeing with him. In truth, such overreach would energize Republicans, drive many independents into opposition, and discourage working- class Democrats already dubious about the effects of illegal immigration on their communities.
Each midterm election takes a different form, even if virtually all of them end the same way, with big losses for the party in the White House. To their credit, Democrats did not take this election for granted.
They understood they could lose, so they prepared by muscling up with money and organization. They have aggressively attacked their Republican opponents.
But this is offset by their failure—or inability—to distance themselves from Mr. Obama. Still to be determined is the quality of the Republican campaigns, especially each candidate's financial strength and ground game.
Many races—like those in Alaska, Arkansas, Colorado, Iowa, Louisiana and North Carolina—will be settled by a couple of percentage points or even a few thousand votes. The election will come down to whether people want allies of Mr. Obama and Sen. Harry Reid returned to Washington—or whether Republicans can convince voters that they will govern, that they are more in touch with the middle class about changing Washington. and that they will better represent their state's values.
Republicans seem to have three Democratic seats likely flipped—Montana, South Dakota and West Virginia—and while it won't be pretty or overwhelming, three to five more seats look like they will fall the GOP's way. If Republicans hold on to Kentucky and Georgia, as appears increasingly likely, that will be enough to kick out Harry Reid, install Mitch McConnell as Senate majority leader, and rein in Mr. Obama during his last two years in office.
A version of this article appeared August 28, 2014, in the U.S. edition of The Wall Street Journal, with the headline Countdown To Kicking Out Harry Reid and online at WSJ.com.