If two people have their feet set in concrete, neither can move very far. That is true in life and especially when serving in the United States Congress.

Last week, Representatives Tim Holden and Jason Altmire, both moderate Democratic congressmen from the state of Pennsylvania, were defeated by liberal primary challengers.

In Indiana, long-time Republican Senator Richard Lugar is facing a primary challenge from a more conservative Republican. Polls have him losing.

In Utah, Republican Senator Orrin Hatch, another giant of the Senate, is also facing a serious primary challenge from a more conservative politician.

In the 2010 midterm elections, dozens of moderate Democrats, and even some moderate Republicans, lost their House seats to tea party Republicans, who are certainly passionate about politics but can’t be considered political moderates in any way, shape or form.

Recognizing a trend?

I am: Political moderates from both parties are gradually disappearing. This, I believe, is the biggest threat facing America — not the national debt, Iran’s nuclear program or the myriad other issues facing the country.

Why? It’s very simple. There are viable solutions to our nation’s problems. But, to get to those solutions, bipartisan deals between Congress and the president need to be struck. Moderates have the political sensibilities necessary to reach across the aisle and make those sorts of deals. As moderates become rarer, reaching bipartisan compromises becomes harder.

Take, for instance, the growing national debt. The only way to get a handle on that debt is to do two things: cut spending and raise taxes. Obviously, there needs to be a balance between the two. If we raise taxes too much, we will damage the economy by reducing people’s disposable income and undermining incentives to work and invest. But cutting spending too much could also damage the economy and, by doing so, reduce tax revenues.

A compromise, where Democrats accept responsible cuts to entitlement programs like Medicare and Medicaid, and Republicans accept reasonable cuts to defense spending and agree to raise taxes on many Americans, would put our nation back on a sustainable fiscal track. But neither party is doing anything serious to make this happen.

Part of the problem is that congressional districts are gerrymandered to protect incumbents. When a politician knows that 70 percent of the voters in his district belong to his party, he has little incentive to compromise on key issues. We need to figure out how to depoliticize the congressional redistricting process so that more members of Congress are forced to win over moderate voters.

None of this seems like rocket science to me. But for some reason the need to elect politicians willing to compromise has been lost on most voters. I hope things change soon, because if they don’t, the serious problems America is facing won’t be resolved.

Ronnie Shows is a former Democratic member of Congress and member of the Blue Dog Coalition. He represented Mississippi’s Fourth Congressional District between 1999 and 2003.