Some people have made the legitimate point that you cannot copy or imitate the solutions of 1981 for 2009's challenges.

While imitation or direct copying a generation later will not work, learning the core principles of Mr. Reagan and learning the lessons of history is essential.

The heart of conservatism ought to be a deep respect for the past and a willingness to think profoundly about how great leaders have met challenges and solved problems in their era.

Because of our deep respect and affection for Mr. Reagan, Callista and I joined with Dave Bossie and Citizens United to make a film, "Ronald Reagan: Rendezvous with Destiny."

That 90-minute documentary reminds us of the charismatic power and extraordinary educational capabilities Mr. Reagan brought to the presidency. The film also has a brief segment that reminds us of the weakness and destructiveness of the left during the Carter presidency.

There are some similarities to the 1977 world in which Jimmy Carter entered office with great popularity (actually more popular than President Obama on Inauguration Day). President Carter followed left-wing policies of increased government spending, government controls of the economy and weakness abroad.

By 1980, these policies of the left had created a disaster. There was 13 percent inflation, 22 percent interest rates, gasoline rationing (Americans were only able to get gasoline every other day based on the last digit of your license plate) and weakness abroad, leading to aggressive Soviet adventurism and a 444-day Iranian hostage crisis.

Under Mr. Carter, America became a mess. And what was his answer to the mess? Mr. Carter gave a national speech telling us to lower our expectations and accept a limited future of malaise as the best we could do. We were told to accept our mediocre fate.

The American people preferred to reject both malaise and Mr. Carter. They elected Mr. Reagan in a landslide and gave him a Republican Senate and a 33-seat increase in the House of Representatives.

The rest was history.

However, the longer I study this period the more convinced I am that while we have much to learn from Mr. Reagan, the lessons of that era are inadequate to the coming crisis.

It is now obvious that despite the great achievements of the Reagan revolution and the Contract with America, there was a strategic failure to root out the left and the special interests of the left.

The result is that 29 years after Mr. Reagan's great victory, the left is stronger in academe, the news media, the courts, the bureaucracies, the interest groups and their lobbyists.

Sacramento, Calif.; Albany, N.Y.; and Trenton, N.J., are sicker today than they were in 1980. The city of Detroit is sicker today than it was in 1980. The willingness of judges to be overtly anti-religious and to imitate foreign courts is greater. The academic world has metastasized so that anti-American leftists and terrorist-group members like William Ayers can get 3,000 professors to sign a letter endorsing them.

The Obama administration has appointed five attorneys whose law firms were pro bono representatives of alleged terrorists. Defending terrorists is in vogue. Defending America is irrelevant.

In this world, essential lessons must also be learned by studying Prime Minister Margaret Thatcher. I strongly recommend "There Is No Alternative: Why Margaret Thatcher Matters," by Claire Berlinski as a starting point.

Mrs. Thatcher clearly understood that the great threat of socialism was moral and not economic. Socialism is bad because it destroys freedom. It destroys self-reliance, destroys individual initiative, and transfers power from the citizen to the politician and the bureaucrat.

Every American who wants to know how dangerous it is for the government to have such enormous influence over AIG, Citibank, Chrysler, etc. should read Ms. Berlinski's study of Mrs. Thatcher.

The evils of socialism and the virtues of freedom will be the central choice for Americans in 2010 and 2012, and Mrs. Thatcher will be our tutor in that argument.

We need Reaganesque optimism and Thatcherite intellectual clarity to defeat socialism and uproot it from the institutions it now controls.

• Newt Gingrich is a former speaker of the House and chairman of American Solutions.