Sens. Pat Toomey (R-Pa.) and Joe Manchin (D-W.V.), the two sponsors of the bipartisan gun background check legislation coming to a vote this afternoon, admit they don't have the votes for passage.

But why would a proposal with near 90 percent support of the American public fail?

Here are five reasons:

1. Senators knew the bill would likely be killed in the GOP-controlled House of Representatives. Most senators are averse to making risky votes but no one will stick their neck out when they know the bill isn't going anywhere.

2. The proposal needed more than a majority to pass in the Senate. Thanks to Senate rules, you need 60 votes to break a filibuster.

3. A majority of Americans in a poll isn't the same thing as a majority in Congress. Despite what you might have learned in grade school, our political system isn't really representative of the population. The Senate gives much more power to those who live in rural areas over those who reside in cities.

4. Unless there is a public backlash against Congress for supporting a popular proposal, special interests with influence like the National Rifle Association will continue to drive the agenda on Capitol Hill.

5. President Obama is too polarizing on the issue of gun control. As we've seen time and again over the last four years, the president's vocal support of an issue is usually enough to galvanize the opposition.

But don't be too disheartened if you were a supporter of the bill. As Jonathan Chait notes, "Our political system is still way better than North Korea's."