Staying home on Election Day carries a heavy cost.

In Ferguson, Mo., where only 12 percent of voters showed up in the last city election, the cost of nonparticipation was a City Council wholly unrepresentative of the town’s population. On the national level, Democrats and independents — most of whom did not vote in the 2010 midterm Congressional elections — were swamped by Republicans who voted in much larger proportions. The result was a Republican House dominated by the hard right, which over four years became the largest impediment to economic growth and equality. The same thing has happened in many statewide elections.

It’s now seven weeks from the midterms. Will voters realize that decisions made on Nov. 4 will reverberate in laws not passed, roads not built and jobs not created?

The biggest prize at stake in November is the Senate, where Democrats are in serious danger of losing control to a Republican Party determined to roll back much of the social progress of the last six years, and to block as many of President Obama’s judicial appointments as possible. There is little chance that Democrats will win back the House this year, in part because of Republican redistricting, but many statehouses and governorships that control districting and voting regulations are also in the balance.

All of that makes it imperative that the demographic groups that turned out in relatively large numbers during the last two presidential elections show up at the polls this year. According to Catalist, a data analysis company, the groups with the biggest declines in turnout between 2008 and 2010 were voters younger than 30, down nearly 35 percentage points; black and Hispanic voters, down 27 points each; and single women, down 26 points. Those groups have historically been the most resistant to the right’s message of lower taxes, sharply reduced spending on social programs and job creation, and tighter restrictions on women’s reproductive rights.