Karl Rove, who masterminded the last two Republican victories in presidential elections, is gazing with undisguised relish at the giant target being painted on Barack Obama's back before the next one.

In an interview with The Times yesterday, he described the likely Democratic nominee as a “frail” candidate, who represents the values of an out-of-touch liberal social elite and demonstrates “tone deafness” to the concerns of ordinary Americans.

“You have probably seen this kind of guy at London parties, trailing ash from a fashionable cigarette into the carpet and making snide remarks about someone ‘being an abominable bore’,” Mr Rove said.

He suggested that voters have not heard the last of Mr Obama’s recent comments at a San Francisco fund-raiser, where he suggested small town Pennsylvanians were clinging to guns and religion because they were “bitter”.

The candidate sounded, Mr Rove said, as if he was following in the footsteps of his anthropologist mother “reporting on the exotic species of voter he had encountered in some dark corner on the opposite side of the globe”.

All this is a far cry from just a few short weeks ago when Mr Obama’s soaring oratory — his promise to heal racial divisions or transcend the partisan politics of an older generation — had Republican strategists regarding him with shock and awe.

It is now the Democrats’ turn to worry. Mr Obama’s decisive defeat in this week’s Pennsylvania primary has been followed by whispers of alarm that they may end up with a candidate who is listing badly — even holed below the water line — just as he is about to cross the finishing line in his race with Mrs Clinton. His failure to win white working-class voters in states like Ohio and Pennsylvania — both certain to be important battlegrounds in November’s general election — has raised doubts about his fitness for the fight against John McCain. He sometimes appears drained by his fight with Mrs Clinton, a woman 14 years older than him, taking time off the campaign trail this week and setting himself a light schedule for the coming days.

Whereas he once energised rallies with the chant, “Fired up! Ready to go!” he now complains about feeling tired and the length of primary season, or says he wants to go home to see his young family.

If Mr Obama loses again in Indiana on May 6, then panic will spread through the party. His campaign spent much of yesterday explaining to the Democratic super-delegates — who could yet wrest the nomination away from him, why he remains the best candidate to beat the Republicans. Mr Obama himself was busy shoring up his battered Everyman credentials by holding a press conference at an Indianapolis petrol station.

But Mr Rove said that “unless something extraordinary happens”, Mr Obama’s lead among elected delegates still means that he will be the Democratic nominee.

And, although it may be unwelcome right now, Mr Rove even had some advice for him. First, he cease making attacks on Mrs Clinton and Mr McCain, which are “corrosive of his fundamental message about representing a new kind of politics”.

Mr Rove also pointed out that Mr Obama cannot stand on a platform promising post-partisan politics when he has virtually nothing to show on this front from sitting in the Senate for three years.

“He should spend less time on the campaign trail between now and September and more time in the Senate” trying to get such an achievement under his belt, Mr Rove said. “The best way to prove a message is to live it.”

Mr Obama has also been embarrassed in recent weeks by his black liberationist pastor Jeremiah Wright, who returned to the airwaves yesterday to denounce the media for portraying him as “some sort of fanatic”.

Unhelpfully, he explained that one of the differences between him and Mr Obama is that he “goes out as a politician and says what he has to say as a politician”.

It is a treacherous, racially-charged subject, and Mr McCain has been careful this week to disassociate himself from Republicans who have launched a TV advert attacking Mr Obama’s links with the pastor.

But Mr Rove suggested that race, far from hurting Mr Obama probably works in his favour by attracting white voters who regard the prospect of a black president as a “hopeful thing”.

A bigger problem for Mr Obama, he said, is winning industrial states like Ohio, Michigan and Pennsylvania with a voter base that resembles “George McGovern's coalition of college students and white wine sippers”.

Mr Rove cited polls showing that as many as 26 per cent of Mrs Clinton’s supporters will vote Republican if Mr Obama is the nominee, saying even though such numbers were likely to come down before November, “there are going to be significant numbers of defections in this contest”.

His scorn for Mr Obama was almost palpable as he described how the candidate had developed a habit of “parsing” when faced by criticism or complaining about rough treatment as he did after last week’s TV debate against Mrs Clinton.

This makes him look like a whiner, Mr Rove said. “She has been getting tough with him — but it's not as tough as it will get from all sorts of places in a general election.”

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