The Republican presidential candidates love the Constitution, but if they have their way, you'll barely recognize it. Like a plastic surgeon meeting with a prospective patient, they see all sorts of ways it could be vastly improved.

Rick Santorum favors a constitutional ban on abortion. Mitt Romney has endorsed an amendment to require a balanced federal budget. Both support a constitutional ban on same-sex marriage.

They are no match for Newt Gingrich. He not only favors a balanced-budget measure but has previously supported changes to limit congressional terms, outlaw flag-burning, promote prayer in public schools and deport mouthy ex-wives.

Ron Paul proposes to limit federal spending and taxes, as well as repealing the 16th Amendment (income tax) and the 17th Amendment (popular election of U.S. senators). Rick Perry had a different amendment for each day of the week.

Leave aside for the moment the wisdom of such revisions. The important thing to keep in mind is that none of these candidates, if elected, will bring any of them to pass. The chance is not small. The chance is zero.

The balanced-budget amendment has been around for some 40 years without getting anywhere. Likewise with the proposed abortion ban. It materialized after the Supreme Court's 1973 Roe v. Wade decision and is no closer to adoption today than it was then.

If there were sufficient support for a balanced budget to amend the Constitution, it would be superfluous, because Congress would take the steps needed to eliminate deficits. Amazingly enough, it did exactly that in the 1990s.

When it comes to abortion, on the other hand, Gallup has found a majority of Americans has consistently been against an amendment to forbid all abortions (except to save the mother's life). That hasn't changed, and there is no reason to think it will anytime in the foreseeable future.

When Gingrich became Speaker after the 1994 Republican takeover of the House, the GOP had a clear mandate for the term-limits amendment, which had been part of the "Contract with America" it rode to victory. It was a popular idea that had been adopted in 22 states, but the amendment fell short in the House.

The flag-burning amendment, a response to a Supreme Court decision ruling that desecration of Old Glory was protected by the First Amendment, attracted strong public support. But it failed repeatedly before fading away.

Amending the Constitution was meant to be hard, which is why it's happened only twice since 1968. Any president looking at this record of futility would find plenty of reasons not to try.

One is that he's highly unlikely to succeed, and presidents don't look for opportunities to lose. Getting a constitutional amendment requires mobilizing a strong national consensus on a particular issue. It requires persuading each house of Congress to muster a two-thirds vote in favor of a specific proposal. And it requires ratification by three-quarters of the states.

Even if the amendment had a plausible chance of passage, it would probably take longer to achieve than a president's tenure in office. He would use up a lot of precious time and political capital that could be devoted to more achievable goals, with more immediate rewards. All this would get in the way of pragmatic, incremental changes.

It may make sense for pro-life groups to hold out hope of a constitutional amendment, since they are in the fight for the long haul. It makes much less sense for a president, who will be gone in four years or eight.

In some cases, a proposed amendment would give members of Congress an excuse to put off serious legislative action. You can prove you're serious about the government debt by voting to raise taxes or cut spending. But that means antagonizing voters who would have to endure unwelcome sacrifices.

So why bother? It's much easier to demonstrate your fiscal conservatism by voting for a balanced-budget amendment—while opposing the actual fiscal changes it would require. Anti-abortion candidates can endorse an amendment without much risk, since pro-choice voters know it's not going to pass.

When a presidential candidate vows to amend the Constitution, he may be doing any number of things: dodging a tough issue, pandering to a bloc of voters or trying to sound bold. What he is not doing is telling the truth.

Steve Chapman blogs daily at newsblogs.chicagotribune.com/steve_chapman

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