By Kevin Anderson
BBC News Online, Washington
President George W Bush had been facing enormous pressure from religious conservatives to take a strong stand opposing same-sex marriage.
Bush says marriage must remain a union between a man and a woman
His support for a constitutional amendment banning gay marriage is sure to keep this key Republican constituency in the fold, but it is a move not without political risk.
The danger for President Bush is that while more than two-thirds of Americans oppose same-sex marriage, only the slimmest of majorities support a constitutional ban.
And Mr Bush's desire to be seen as a compassionate conservative could be endangered if the debate turns poisonous, a throwback to the culture wars of the 1990s.
Shoring up support
For Mr Bush, this was a simple case of so-called base maintenance, shoring up his political base as he begins his bid for re-election in earnest.
For weeks, religious conservatives had been imploring Mr Bush to take a strong stand against same-sex marriage following a Massachusetts state Supreme Court ruling clearing the way for gay marriage.
And the mayor of San Francisco's decision to grant same-sex marriage licenses only angered conservatives more.
It was a simple decision for Mr Bush. A FoxNews poll found 80% of Republicans oppose same-sex marriage.
US CONSTITUTIONAL AMENDMENTS
US constitution has 27 amendments
Amendments require passage by Congress and ratification by three-quarters of US state legislatures
Last amendment ratified in 1992, saying pay rises for representatives and senators cannot come into effect until after an election (this amendment was originally passed by Congress in 1792)
First 10 amendments collectively known as the Bill of Rights
Only one amendment has ever been repealed - Prohibition - by a subsequent amendment
And little now is required of Mr Bush. The president has no constitutional role in passing an amendment.
The process will be difficult. The framers of the constitution set a high bar for amendments.
Both Republicans and Democrats say the amendment has no chance of being ratified quickly and little chance of being ratified at all.
But as Dennis Hastert, the Republican leader in the House of Representatives, said, the president can win by losing.
Mr Bush is able to draw a stark distinction between himself and his Democratic rivals.
Senator John Kerry, leading contender for the Democratic Party's presidential nomination, criticised Mr Bush saying that he was trying to use the issue to divide Americans.
"This President can't talk about jobs. He can't talk about health care. He can't talk about a foreign policy, which has driven away allies and weakened the United States, so he is looking for a wedge issue to divide the American people," Mr Kerry said.
Republicans see Democratic frontrunner John Kerry as vulnerable on the issue
But Republicans see Mr Kerry as vulnerable on the issue. He was one of only 14 Senators to vote against the Defence of Marriage Act in 1996.
That act said that states did not have to honour a same-sex marriage conducted in another state.
But Mr Bush also faces his own political risks by pressing this issue.
While polls show that two-thirds of Americans oppose same-sex marriage, only a slight majority support an amendment to ban same-sex marriage.
And if the debate turns poisonous, both he and the Republican Party could once again be viewed not as compassionately conservative but as mean-spirited and intolerant.
That is why Mr Bush said when he announced his support for the amendment, "We should also conduct this difficult debate in a manner worthy of our country, without bitterness or anger."
Mr Bush remembers only too well Pat Buchanan's speech at the 1992 Republican Convention as his father launched his re-election bid.
Despite George HW Bush's desire for a kindler, gentler nation, many Americans remember Mr Buchanan's calls for a culture war.
George W Bush knows he will win re-election by convincing Americans that he is winning the war on terror and not by restarting the culture wars.