The Orange Revolution has hit a bump. And it might be big.

Viktor Yushchenko's chief of staff Oleksandr Zinchenko quit, and quit noisily, claiming that members of the Yushchenko government are corrupt.

"With my resignation I am trying... to make both the president and his team understand the grave danger of the current situation," Mr Zinchenko told a news conference in the capital, Kiev.

"Now corruption and bribe-taking are growing in force," he said.

Mr Zinchenko specifically named Ukraine's National Defence and Security Council head Petro Poroshenko and senior presidential advisor Olexandr Tretyakov.

He accused the two men of nepotism and also pressure on the judiciary.

He warned that the president could face a "counter-revolution" if he did not fire Mr Poroshenko and Mr Tretyakov.

Yushchenko thought enough of this action that he cancelled his trip to Poland this week, and circled the wagons by bringing his long-time trusted aide Oleh Rybachuk to replace Zinchenko.

The Ukrainian president's hands are tied because, if he sacked any of the officials at the heart of the corruption allegations, he would risk upsetting the delicate balance of power inside his administration, said analyst [Yuri] Yakimenko.

"Those who are already in power are likely to remain in their jobs. For a month or two the situation will remain unchanged," he said.

The delicate balance, which I described last spring, emboldens prime minister Yulia Tymoshenko, who is trying to keep the prime minister's post past the March elections, when it will have far more power than it currently does. There is discussion now that Tymoshenko has prepared a list of candidates for the parliament in case Yushchenko does not back her further from here. She would probably be difficult to beat.

She may well join forces with Poroshenko, who is often referred to as the "Chocolate King" and has a pretty fat bank account that would help with the campaign. The result could be a weakened presidency for the final three years of Yushchenko's term.

All this probably probably wish they had a journey of their own.