For a year, the big question in political circles has been whether Tuesday’s midterm elections will be a Republican “wave.” Optimistic conservatives and GOP operatives say (and hope) yes; concerned Democrats and annoyed liberals say (and hope) no.

These are terrible conditions for Democrats. The president’s approval rating hovers in the low 40s. Two-thirds of the country thinks it’s on the wrong track. Polls show Americans now trust Republicans more than Democrats on more issues of concern than at any time since 2006.

Taken together, these should be like boulders tied to the legs of Democratic candidates, weighing them down and effectively drowning their hopes.

And they are — but in fewer cases than most people expected.

Republicans need to gain a net six seats to take control of the Senate. They are assuming they have three of those seats in the bank (in West Virginia, Montana and South Dakota), and so they must rack up three more to take control of the Senate.

They will likely win the Democratic Senate seat in Arkansas, where the Republican candidate seems to be pulling away from the sitting Democratic incumbent. 

This leaves them fighting tooth and nail over six other Senate seats held by Democrats: Colorado, Iowa, North Carolina, New Hampshire, Alaska, and Louisiana. Meanwhile, a Republican seat in Georgia is in play. And an independent candidate (who is basically a Democrat in sheep’s clothing) is giving a tired Republican incumbent the fight of his life in Kansas. 

If there’s a “wave” on Tuesday, almost all of these will go the GOP’s way. That’s what a wave means — a national tide that directs results in a single direction. If that doesn’t happen, Republicans will probably win enough to take control of the Senate and claim a big victory.

But even if they do well enough to get the Senate, the truth is there ought to be a GOP wave, and everyone knows it. If there isn’t, even a net gain of seven Senate seats will not only be a mild disappointment for the GOP but also something that is liable to engender a quiet panic among Republican professionals.

If the party cannot win handily in this atmosphere, Republicans will plunge into the depths of a despair we won’t have seen in American politics since Democrats had to crawl out of the wreckage of the 1984 presidential election.

That despair won’t be about the goings-on in Washington for the next two years. In fact, when it comes to national policy, it won’t matter all that much whether the wave emerges or not.

Barack Obama will still be president. Republicans will still dominate in the House. Even if the GOP takes control of the Senate, conservative legislation will not get past Obama’s veto pen. What’s more, if by a miracle Democrats retain the Senate, the gridlock that has frozen Washington in place since 2010 will remain because House Republicans will not assent to liberal initiatives.

So why is this election so important?

Simple. It is a guidemap to the future — to the election of 2016 and beyond. 

We will be given an answer to the most pressing question in American politics: Has the amazing machine Obama built to get himself elected president in 2008 and re-elected in 2012 been successfully repurposed to work for the Democratic Party overall?

Obama built a powerful constituency. In both elections, he got the votes of the young by a margin of 2-to-1, the votes African-Americans by a margin of 97-3 (at turnout levels higher than those of white voters), and the votes of other minorities in the 60 to 80 percent range.

That constituency did not show up at the polls in the 2010 midterm elections and the result was the most one-sided election (from Washington through the states) of any since 1928. What’s more, the Obama constituency showed up in smaller numbers in 2012 than it had in 2008. The president received 4 million fewer votes in his re-election bid than he had in his first race, but still beat Mitt Romney by nearly 5 million.

After 2012, the Democrats were determined to solidify the Obama constituency and see if it could be harnessed to some degree in the midterm — which, in turn, would suggest it could be reconstituted en masse in 2016.

To that end, it launched a $60 million effort called the Bannock Street Project, named after the street on which a brilliant campaign was run in 2010 in Colorado that won a Democrat named Michael Bennet a Senate seat he probably had no business winning. Combining the Bennet strategy with the Obama constituency would provide Democrats with a storm wall high enough to repel a Republican wave.

The data have long suggested the effort is paying off dividends. 

Republicans are doing well. But the point is that Democrats aren’t doing badly. They are hanging on in state after state, the polling suggests. And if they do better than just hang on, it will be because they will have brought voters to the polls on Tuesday who otherwise would never have shown up.

The secret of the 2012 election was that Obama’s campaign succeeded in dragging very unenthusiastic Democratic voters to the polls in defiance of all conventional expectations.

In previous elections, highly unenthusiastic voters just stayed home, which is what the Romney people thought would happen again. But as Romney pollster Neil Newhouse ruefully says, if you get him there, an unenthusiastic voter’s ballot counts the same as a highly committed partisan who drags himself over hot coals to get to the polling booth. 

So even if you don’t care who the senator from Colorado is going to be; even if you don’t care what’s going on between the Democrat and the Republican in Alaska; even if you don’t care whether there will be a runoff in December in Louisiana or a runoff in Georgia in January; maybe you should. 

A Republican wave won’t guarantee a Republican victory in 2016 by any means, but it will give Republicans a huge opening to advance their arguments about the best approach to America’s future.

They will have a real opportunity to capture the public’s ear not only about the failings of the Obama administration but also about how to move beyond them — to make the arguments that American leadership in the world must be reasserted, that there are non-statist approaches to address middle-class wage stagnation and the uncertain economic future, and that there are workable alternatives to the ObamaCare disaster.

They will have a much harder time doing so if there is no wave, because that will demonstrate structural GOP weakness and long-lasting Democratic vote-getting strength. And yet those longer odds will make the task of reforming and refining and winning these arguments about America’s place in the world and its economic and fiscal health all the more urgent.