The trouble began in earnest in September, when Yanukovych refused to implement seven presidential decrees, arguing that they were issued without his cosignature. Yanukovych, in return, demanded that President Viktor Yushchenko sack five regional governors loyal to the president.
Yushchenko later declined a recent invitation by Yanukovych to participate in a cabinet ministers meeting. Most recently, of course, the president's Our Ukraine bloc appeared to dismiss the possibility of joining the ruling coalition led by Yanukovych's Party of Regions.
Both politicians have apparently entered a period of argument over who is to play the leading role in Ukraine's constitutionally remodeled political system, which went into effect this year.
The constitutional amendments were hastily adopted in December 2004 to resolve the presidential-election standoff between Yushchenko and Yanukovych against the backdrop of the Orange Revolution. They now seem to have backfired, devolving into an institutional row between the two leaders. It Sounded Good On Paper
The constitutional requirement that some presidential decrees should be cosigned by the prime minister and the ministers directly responsible for their implementation existed even before the 2004 reform.
Despite their rivalry, Yushchenko and Yanukovych may be forced to cooperate with each other in the future.
But in the era of former President Leonid Kuchma, no prime minister -- including both Yushchenko and Yanukovych -- ever invoked the attendant provision to question the legality of presidential decisions.
Now, however, the situation is different.
The constitutional reform, which took effect on January 1, 2006, has shifted the center of political power from the president toward the prime minister and parliament, making the president and the prime minister top executive officials with more or less equal authority.
President Yushchenko and Prime Minister Yanukovych are from different political camps, so it is hardly surprising they are now competing for recognition as the uppermost politician in Ukraine.
But since both politicians personify opposing sides of Ukraine's deeply felt East-West divide, their rivalry, if continued, will no doubt contribute to widening this troublesome gap. No Easy Way Out
Yushchenko proposed a solution two months ago when he persuaded the Our Ukraine bloc to enter a government run by Yanukovych's Party of Regions jointly with the Socialist and Communist parties.
Even more significantly, Yushchenko succeeded in convincing all major political parties -- except for the Communists -- to sign the so-called declaration of national unity on basic foreign and domestic policies. With that, the signatories pledged to continue Ukraine's course toward integration with NATO and the EU.
This solution, however, proved to be short-lived.
Last month in Brussels, much to Yushchenko's surprise and chagrin, Yanukovych announced that Ukraine was not ready to join NATO's Membership Action Plan because of low public support for NATO entry.
Yushchenko condemned this announcement as "wrong" and being at variance with national interests.
And on October 4, following a failed round of talks on a new coalition agreement, Our Ukraine leader Roman Bezsmertnyy announced the bloc was switching to the opposition and asking its ministers to quit Yanukovych's cabinet or to renounce their party affiliations if they want to stay.
"Today the negotiating process was concluded," he said. "I don't know whether it is a happy or unhappy piece of news, but -- thank God -- all participants in this dialogue have made a decision. There is a government coalition, and there is Our Ukraine, which is in opposition to the government coalition." Support Base Dwindling
Our Ukraine has four ministers in the current cabinet: Justice Minister Roman Zvarych, Family and Sports Minister Yuriy Pavlenko, Culture Minister Ihor Likhovyy, and Health Minister Yuriy Polyachenko. If they resign, President Yushchenko will lose further control of a government that has already started to oppose his policies.
And there may be even more unpleasant developments in store for the president.
Apart from the Our Ukraine ministers, two other Yushchenko men are in Yanukovych's cabinet -- Foreign Minister Borys Tarasyuk and Defense Minister Anatoliy Hrytsenko. The president is legally required to appoint both those posts.
But with Our Ukraine bloc members joining the opposition -- including the People's Rukh of Ukraine, which is headed by Tarasyuk -- it stands to reason that Tarasyuk may quit the cabinet.
That would be a major loss for Yushchenko; Tarasyuk is a staunch promoter of Ukraine's integration with Europe.
Hrytsenko, who has no formal party affiliation, is likely to retain his job. Signs Of Compromise
Our Ukraine's failure to strike a deal on a grand coalition could potentially turn into a serious setback for Yushchenko's policy of rapprochement with the West.
But Yanukovych also has reason to be concerned. His cabinet is critically dependent on the parliamentary support of Marxist-oriented Socialists and Communists. They may ultimately force the prime minister to make his agenda "more leftist," abandon his liberal economic course, and slow down pro-market transformations in the country -- policies that Our Ukraine, by contrast, might be likely to support.
This is perhaps why Yanukovych tried to play down the failure of the grand coalition talks and suggested that not everything had been lost in this regard.
"I'm sure that we have not yet completed this process" of building a broader coalition, Yanukovych said on October 5. "President Yushchenko, with whom we reached agreements, remains and will continue to be Our Ukraine's leader, and that the de facto representatives of Our Ukraine in the government are working in accordance with our agreements."
The same day, in a press release, Yushchenko met Yanukovych halfway, emphasizing his belief that participants in the grand coalition talks "still have a chance of reaching agreement on key issues." Bound To Cooperate
It seems therefore that despite their evident rivalry, Yushchenko and Yanukovych will be forced to cooperate with each other in the future, regardless of what happens with the current ministers from Our Ukraine.
Yushchenko possesses a power of veto over legislation, while the Yanukovych-led coalition falls 60 votes short of the 300 votes required to override it.
On the other hand, Yushchenko cannot take any meaningful steps toward bringing Ukraine closer to the EU and NATO without the consent of Yanukovych's Party of Regions.
For purely practical reasons, such a situation should push both politicians toward forging a modus vivendi based on political compromise. Otherwise, Ukraine will be left with two sets of policies and two separate centers of authority -- one applauded in the west of Ukraine, the other in the east.