The public's frustrations with politicians cross ideological lines. But before imagining that a small number of votes - including yours - can't make a difference, consider a high-profile result from last Tuesday's Republican primary in Mississippi.

State Sen. Chris McDaniel edged six-term incumbent U.S. Sen. Thad Cochran by fewer than 500 votes. But Mr. McDaniel's 49.6 percent (Sen. Cochran got 48.9 percent) fell just short of the majority needed to avoid a June 24 runoff.

Most of the punditry reaction to that outcome focuses on the Tea Party's support of Mr. McDaniel and the Republican establishment's support of Sen. Cochran.

But regardless of which party, if any, you support, that close call in Mississippi re-confirms that relatively few voters really can have a decisive voice in public policy - and that non-voters can't.

That's particularly pertinent in U.S. Senate races this year. Expert consensus now gives the GOP a serious shot at regaining Senate control for the first time since losing it in the 2006 elections. And with Democrats having virtually no realistic chance of winning back the House, that would put Republicans in charge of both chambers of Congress.

So don't forget Tuesday's South Carolina primaries for the U.S. Senate and other offices.

And don't accept the false premise that your vote doesn't count.