Governor Carnahan was a popular governor

Missouri is a key state for the Democrats, who need a net gain of just five seats in next month's election to take the Senate. It is one of seven states, out of the 34 up for election, where a Democrat gain is a real possibility.

Governor Carnahan was killed in a light aeroplane crash on Monday, along with his son Roger and campaign adviser, Chris Sifford.

At Tuesday night's presidential debate between Al Gore and George W Bush there was a minute's silence. Both men cancelled post-debate rallies that they had held after their previous encounters.

"This debate in a way is a living tribute to Mel Carnahan because he loved the vigorous discussion of ideas in our democracy," said Mr Gore, extending his sympathy to the victims' families

Mr Bush also offered prayers and blessings and said: "It was a tragic moment."

Campaign suspended

Mr Carnahan was a very popular second-term politician, giving Mr Ashcroft a run for his money. Both had large campaign funds and a strong record in winning state elections.

They had been rivals for 20 years and this campaign had often become bitter and personal.

Mr Ashcroft has suspended his campaign as a mark of respect, at least until after the funerals. His campaign website has been replaced with a simple statement.

"This is a time for unity and common purpose in our state," it says. "That our Senate campaign could have ended so tragically is shocking."

No decisions are likely to be made until after the funerals and memorial services. But some sort of political campaign could yet re-ignite.

The options

Under Missouri law, Mr Carnahan's name cannot be removed from the ballot papers. If he gets the most votes, a Democrat could be chosen to serve, either until the next general election in November 2002, or for the full six-year term.

The presidential candidates share a moment of silence for Mel Carnahan

That task would fall to Lieutenant Governor Roger Wilson, who was sworn in as governor on Tuesday and will serve out the remainder of Mr Carnahan's term, which ends on 8 January. Because the new Congress is sworn in on 3 January, the newly elected governor will not yet have taken power.

This eventuality could anger Republicans and spark a legal challenge. They could argue that a dead man could not run in an election.

One possibility is that Governor Wilson, in consultation with Democratic leaders, might announce his choice before the 7 November election. That way, voters would know in advance who the choice of candidates were.

It would also lessen possible Republican bitterness that a governor, who was himself un-elected, could make such a decision.

But it is all speculation. Mr Ashcroft was always in a good position for re-election, and without his tough opponent he could reasonably expect to win. For the time being at least, politicians are united in mourning a popular man.