A rule of electoral politics is that when a Democratic wave is building, the media broadcast it like a foregone conclusion. When a Republican wave is building, Beltway pundits are the last to admit it. After Tuesday's GOP win in a Florida special House election, even the press corps now agrees that Republicans are poised for major gains in November, assuming the GOP has the wit to exploit it.

Democrats are spinning the defeat as no big deal, but no one outside the MSNBC mind-meld believes that. Democrats got their preferred candidate in Alex Sink, who had barely lost the governor's race in 2010, and she outspent Republican David Jolly, a former Congressional aide and lobbyist who endured a rough January primary. Political seers Sean Trende andLarry Sabato had predicted a Democratic victory.

The race also showed the renewed threat that ObamaCare poses to Democrats. Ms. Sink wasn't in Congress to vote for the law, but she made the mistake of not running from it. She took the Democratic Party advice to say she'd fix the failing parts of the law even as she attacked Mr. Jolly for supporting repeal. The mend-it-don't-end-it strategy now looks more perilous.

Democrats also rolled out their greatest distraction hits, such as Social Security and Medicare cuts, which Mr. Jolly rebutted effectively. The Democratic class-war line employing the minimum wage and jobless benefits also failed to move enough independents to prevail in a swing district that President Obama had carried in 2008 and 2012.

All of which poses a particular challenge for the ObamaCare Dozen in the Senate who provided the votes to pass the law. Incumbents Kay Hagan (N.C.) and Mary Landrieu (La.) have adopted the mend-it-don't-end-it line, and now they have to decide if they need to support more substantial changes to survive. Democratic interest groups and the White House will say stay the course, but they aren't risking their careers.

Republicans have their own challenge, which is how to turn a good year into one that captures the Senate with seats to spare. With 10 or 11 vulnerable Democratic incumbents or open seats, this is now possible. One obvious point is that the party's factions ought to start targeting Democrats rather than each other. The assault by former Senator Jim DeMint's former aides at the Senate Conservatives Fund on Minority Leader Mitch McConnell won't elect primary challenger Matt Bevin, but it might defeat Mr. McConnell in November. The attacks are about personal feuds rather than policy.

More broadly, the GOP needs a unified House-Senate strategy for how to best exploit its ObamaCare advantage. The repeal message is still potent with the GOP base, but a more positive message would attract independents and frustrated Democrats. Several proposals to repeal and replace ObamaCare wholesale are circulating in Congress, but none has a chance to pass and they all need more debate.

The GOP goal this year should be simpler: Craft legislation that highlights and fixes the flaws in ObamaCare that have been so clearly exposed in the last few months. This means offering plans to repair the damage to the individual insurance market and protect the millions of Americans who have lost their coverage and now must pay more.

Former Senator Phil Gramm suggests that the GOP campaign theme should be the freedom to choose your own health care. Wisconsin Senator Ron Johnson has circulated a memo proposing a strategy around the theme of "freedom and choice."

The details can be debated, but the proposals could include eliminating ObamaCare's mandates that have raised the price of insurance. Most voters have figured out by now that 50-year-olds don't need maternity coverage. Insurance companies should be able to sell any plan they want, and individuals should be able to buy it across state lines. A provision for high-risk pools could address the Democrats' pre-existing condition attack.

The overarching strategy should be to craft a proposal that can unite the party and comfortably pass the GOP House in order to put pressure on Senate Democrats. Any legislation should avoid creating targets for Democrats to change the subject from ObamaCare's flaws. This means avoiding a fight this year over ending the tax exclusion for employer plans in favor of a universal tax credit. Such a reform will never pass while Mr. Obama is President, so Republicans shouldn't take the political risk in 2014. Let the presidential candidates in 2016 take that on.

A modest reform that addressed ObamaCare's most urgent problems would have the benefit of preserving and expanding the individual market until a larger rewrite is possible. Republicans would be able to give voters some hope of relief if they win, without overpromising what they couldn't deliver even if they did control the Senate in 2015.

Like Mr. Jolly in Florida, Republicans also need to talk about more than ObamaCare. Pushing more U.S. energy production and exports is a political winner that creates more jobs and helps America's security. Exposing the costs of President Obama's regulatory assault on business also addresses economic anxiety. And don't forget the IRS.

Current GOP leaders in Congress haven't been very good at strategy, to say the least, but Tuesday's victory underscores the political opportunity that is building this year. An election wave would be a terrible thing to waste.