You can win midterm elections without a positive agenda. You can’t win presidential elections that way. It is therefore vitally important for Republicans to win the Senate in 2014. Here’s why.

In midterms, it’s all right to be the party of no. The 2010 election, for example, was a referendum on the liberal overreach of the first two Obama years. Result? A Democratic “shellacking,” said President Obama. The massive stimulus, (the failed) cap-and-trade and Obamacare created a major backlash that cost Obama the House and, with it, the rest of his ideological agenda. It’s been blocked ever since.

That’s the power of no. And Republicans should not apologize for it. The role of the opposition is to oppose. With the welfare state having reached the outer limits of its competency and solvency, it is in desperate need of restructuring and reform. With an ideologically ambitious president committed instead to expanding entitlements, regulation and government itself, principle alone would compel the conservative party to say stop.

“Stop” was more than enough in 2010. With the president in decline and his presidency falling apart, it will be enough in 2014. Those complaining that Republicans haven’t come up with a national agenda are forgetting that we don’t have a parliamentary system. We don’t have an organized hierarchical opposition with a shadow prime minister and shadow Cabinet. We’ve got 500-odd local political entrepreneurs running under the same Republican banner but offering distinctly independent takes on its philosophy.

The 1994 Contract With America is, of course, the exception. But that required unique leadership and circumstances. We do not have that now.

Nor do we need to. Republicans are today on track to take back the Senate.

Why is this important? It’s not an end in itself. Nor will it change the trajectory of Obama’s presidency. His agenda died on Nov. 2, 2010, when he lost the House. It won’t be any deader on Nov. 4, 2014, if he loses the Senate.

But regaining the Senate would finally give the GOP the opportunity, going into 2016, to demonstrate its capacity to govern.

You can’t govern the country from one house of Congress. Republicans learned that hard, yet obvious, lesson with the disastrous shutdowns of 1995 and 2013. But controlling both houses would allow the GOP to produce a compelling legislative agenda.

The Democratic line is that the Republican House does nothing but block and oppose. In fact, it has passed hundreds of bills only to have them die upon reaching the desk of Senate Majority Leader Harry Reid. He has rendered the Senate inert by simply ensuring that any bill that might present a politically difficult vote for his Democratic colleagues never even comes to the floor.

Winning control of the Senate would allow Republicans to pass a whole range of measures now being held up by Reid, often at the behest of the White House. Make it a major reform agenda. The centerpiece might be tax reform, both corporate and individual. It is needed, popular and doable. Then go for the low-hanging fruit enjoying wide bipartisan support, such as the Keystone XL pipeline and natural gas exports, most especially to Eastern Europe. One could then add border security, energy deregulation and health care reform that repeals the more onerous Obamacare mandates.

If the president signs any of it, good. If he vetoes, it will be clarifying. Who then will be the party of no? The vetoed legislation would become the framework for a 2016 GOP platform. Let the debate begin.

The risk-averse will say, why take chances? Why not just run against the Obama legacy in 2016?

The GOP should and will. What has happened to economic growth, social cohesion and America’s standing abroad will be a significant drag on Democrats. But it could very well not be enough.

Obama won’t be on the ticket. Hillary Clinton, now rapidly distancing herself from the administration she served, will be running on a different legacy, that of her husband and the holiday-from-history 1990s.

Moreover, for winning the presidency to mean something, you need a mandate. Ronald Reagan understood this. He could have coasted to victory in 1980 on mere opposition. But he had a platform, much of which he successfully enacted precisely because he ran on it.

Memo to the GOP: Win the Senate, then enact an agenda and dare the president to veto it. Show the country what you stand for. Then take it to the nation in 2016.

© 2014, The Washington Post Writers Group