Jan Cienski in Warsaw -

Poland's prime minister has a chance to take the most prestigious job a Pole has held since John Paul II was Pope. But as Donald Tusk considers whether to take a stab at replacing Herman Van Rompuy as president of the European Council, the consequences for politics in Poland could be enormous.

Tusk's name came up as a potential candidate during the failed EU summit on July 16/17 - now delayed to the end of August to allow European leaders to choose the Union's top jobs. After the summit, Tusk said he had been approached by "many colleagues" sounding out his interest. He was careful not to rule out a candidacy, saying: "I like to keep every option in reserve."

That sent a shock wave through Polish politics, and particularly through the ruling Civic Platform (PO) party. That's because Tusk has been a key factor in the party's twin electoral victories, handing it the first consecutive administrations since the fall of communism. Without the forceful PM there is a danger PO could lose its electoral locomotive and suffer the fate of so many other Polish political parties by fracturing and disappearing.

Charming and personable, Tusk is also a ruthless political player who has scrubbed his party clean of barons and potential rivals. That means there is no obvious successor.

Parliament Speaker Ewa Kopacz is also the deputy leader of PO, and some see her has a possible replacement prime minister. However, she lacks Tusk's charisma and is not the same calibre of political beast. Other potential candidates include Jan Krzysztof Bielecki, a former prime minster who is currently Tusk's closest advisor, as well as Defence Minister Tomasz Siemoniak. Lurking in the background is Grzegorz Schetyna, at one time a trusted lieutenant and possible successor, now banished to the back benches for his ambition.

Without Tusk at the helm, the party is seen at risk of fracturing into a conservative wing, closer ideologically to the right-wing Law and Justice (PiS)opposition party, and a liberal wing with more in common with the centre-left.

PO is also under growing pressure thanks to the recent "Waitergate" scandal, in which secretly recorded conversations of senior ministers were transcribed in a news weekly. A new opinion poll out this week shows the party's approval ratings sagging, with only 23% support compared to 35% for PiS.

Tusk is seen as a strong candidate to take the Brussels post, thanks in part to his close relationship to German Chancellor Angela Merkel. But if he does get the job, "there would likely be conflicts and splits in PO, which increase the possibility of early elections and the taking of power by PiS," writes Wojciech Szacki, an analyst at Polityka Insight.