The inexorability of Tony Abbott’s rise towards the prime ministership has upset a lot of people, not all of them on the left. Malcolm Turnbull’s frustrations, for example, have long been obvious. Now another prominent Liberal’s disappointment has come into focus, after the ABC’s 7.30 last night aired claims that Peter Costello was so irked by the prospect of Abbott’s success that he had made moves towards engineering a comeback.

The story is attributed to Costello’s long-time friend and ally Michael Kroger. Costello denies it vehemently, and last night publicly confirmed the end of that friendship, saying (as reported in The Age) that “The last thing I would ever do is to give a confidence to Michael Kroger.”

For 30 years, the names of Kroger and Costello have been inextricably linked. They worked closely together as Young Turks on the right of the Victorian Liberal Party in the early 1980s; Kroger went on to win election as state president in 1987, and from that position he helped engineer Costello’s entry to federal parliament in 1990. When the party’s internal consensus fractured in the mid-1990s they remained allies, finally retaking control of the organisation in 2003 when Kroger’s ex-wife Helen became state president.

Things started to fray after Costello turned down the Liberal leadership following the 2007 election defeat. Kroger backed Turnbull, while Costello supported Brendan Nelson. Their followers within the Victorian party started to choose sides, most initially lining up with Kroger. But 30 years is a long time, and many that had started out as protegés of the two powerbrokers began to shuck off their control and develop ideas of their own.

Everyone agrees that last month’s senate preselection was the touchstone for the latest allegations. Helen Kroger had entered the senate after being given second place on the Coalition ticket at the 2007 election, and her ex-husband was determined to keep her there. Media reports before the vote were interpreted as bearing his fingerprints — for example, this piece in the Herald Sun bemoaning the “internal bickering”.

But the party made its view clear, voting by a two-to-one margin to promote Senator Scott Ryan to the No.2 spot and relegate Kroger to the electorally doubtful third. Costello, according to most sources, had stayed out of the contest, but Michael Kroger evidently blamed him for the defeat.

The last straw came on Monday, when The Age published a somewhat over-egged but broadly accurate piece by Katharine Murphy telling the story and proclaiming that “The Kroger era is over.” In revenge, Kroger apparently allowed the ABC to repeat the story of Costello seeking to return to federal Parliament.

There is nothing implausible in the idea that Costello might be “bored and frustrated” and regretting his decision to quit politics. It was a decision he never really explained, and like much in his career it remains somewhat mysterious. Despite the happy conjunction of his name with Abbott’s (and the fact that they were plaintiffs together in a famous defamation case) the two have always been rivals, and the idea of a comeback might have tempted him.

Other parts of the story, however, fail to ring true. Josh Frydenberg, member for Kooyong, would be an unlikely prospect for Costello to think he could persuade to step aside, since Frydenberg was a strong Howard supporter and Costello’s forces opposed him in his first preselection in 2006. The source who told The Age that it “stretches the bounds of credibility” had it about right.

Kroger and Costello between them achieved more than most politicians: Kroger’s presidency gave the moribund Victorian Liberals a much-needed shake-up, and Costello spent 11 years in one of the most powerful positions in Australian government.

Yet each has reason for regrets. Kroger could have become member for Kooyong himself when Andrew Peacock retired in 1994, but he chose to concentrate on his business career and leave the way clear for Costello.

Costello in turn found his ambitions repeatedly stymied both by his own lack of nerve and by factors beyond his control.

Now it seems they don’t even have each other’s friendship for consolation.