President George W. Bush will on Monday meet conservative activists at the White House to underline his support for a constitutional amendment to ban gay marriage, re-inforcing the message of a weekend speech in which he urged Congress to pass the amendment.

Although Mr Bush successfully exploited gay marriage to win re-election, the twin speeches mark the first time since 2004 he has openly promoted the issue. The amendment was not mentioned in his state of the union speech earlier this year.

His intervention comes as the Senate begins a debate on Monday on an amendment to define marriage as a union between a man and a woman. However, the vote, set for Wednesday, is expected to fall short of the 67 votes needed to enact a constitutional amendment. These require approval by two-thirds of each chamber of Congress.

The revival of the issue marks the most visible contours of the electoral strategy being crafted by Karl Rove, the president’s chief political strategist who has been charged with focusing on the mid-term elections. In an effort to rally disaffected Republican conservatives – whose support for Mr Bush has slipped from 91 per cent to 68 per cent – he is turning again to the divisive issues of gay marriage and judicial nominations.

In his radio address on Saturday, Mr Bush combined both themes. He defended marriage as “the most enduring and important human institution” that should not be “cut off from its cultural, religious and natural roots without weakening this good influence on society”.

The speech also included a direct assault on the courts, using the phrase “activist judges” or “activist courts” three times. Mr Bush, who is poised to nominate a new wave of conservative judges, said an amendment was needed “because activist courts have left our nation with no other choice”.

However, there are doubts about whether the issue will be electorally effective. Pat Buchanan, a conservative commentator, said a key difference was that in 2004, outrage over the issue was “authentic” and gained momentum from the decision in May 2004 when Massachusetts began marrying same-sex couples.

There are also only a handful of critical swing states where the issue is on a ballot this November. According to Stateline.org, which tracks state initiatives, Idaho, South Carolina, South Dakota and Virginia will have votes on state amendments on gay marriage approved by the legislatures in November. Wisconsin and Alabama will also have votes this year.

The supreme court of Washington state is expected to rule soon on whether to overturn two lower court rulings in favour of same-sex marriage, “marking the first state high court to tackle same-sex marriage since Massachusetts’ highest court issued its ruling legalising gay unions in November 2003”, says Kavan Peterson of Stateline.