By Lidia Kelly and Pawel Sobczak
WARSAW (Reuters) - In trying to prise former Polish prime minister Donald Tusk out of one of the European Union's top jobs, the ruling conservatives in Warsaw may have another battle in mind: the 2020 presidential election in Poland.
The eurosceptic Law and Justice (PiS) party said last week that Tusk, 59, was unfit to serve another term as European Council president, responsible for chairing EU summits. It has proposed another Pole, European Parliament member Jacek Saryusz-Wolski, to replace him.
Few diplomats expect the PiS to succeed in thwarting Tusk's reappointment, to be decided at an EU summit this week. Some political analysts say its real goal is to tarnish his image at home sufficiently to prevent him from ever threatening its rule.
Tusk's Civic Platform (PO) defeated the PiS in elections in 2007 and 2011 before being unseated by it in 2015 - struggles that have given rise to a bitter rivalry between him and PiS leader Jaroslaw Kaczynski.
"Kaczynski correctly sees Tusk as his most dangerous enemy," said Jaroslaw Flis, a sociologist at Jagiellonian University in Krakow.
Kaczynski, 67, who holds no government post but is seen as Poland's main decision-maker, views Tusk as morally responsible for the death of his twin brother, President Lech Kaczynski, in a plane crash in Russia in 2010.
Investigators have cited pilot error but Kaczynski has said negligence on the part of the government, in which Tusk was prime minister, was at least partly to blame.
On the economic front, the nationalist-minded PiS has accused Tusk's pro-business centrists of neglecting national interests for the sake of better relations with Germany and foreign corporations."There are two mechanisms here," said Aleksander Smolar, a liberal political analyst with the Stefan Batory Foundation, describing the conservatives' efforts to block Tusk's EU job.
"One is revenge. The other is the desire to prevent Tusk from returning to Poland on a white horse, unifying the opposition and eventually winning over the PiS. It's about diminishing his value," he said.
If Tusk wins another 30-month term as EU Council chairman, his mandate would finish around the end of 2019, just months before the 2020 presidential election -- convenient timing if he wanted to run. A parliamentary vote is due in late 2019.
He enjoys wide support among EU leaders, including Poland's allies in central Europe, who see him as a safe pair of hands at a time when the bloc is struggling with challenges like Brexit and the migration crisis.
Kaczynski has branded Tusk the candidate of German Chancellor Angela Merkel and blamed him for failing to work out a compromise deal with Britain that might have dissuaded the UK from voting last year to leave the EU.
Tusk further upset the government back home in Warsaw by criticising it in December over its plans to limit media access to parliament and a controversial reform of the constitutional court. He had decided then to "ostentatiously support the opposition", Deputy Foreign Minister Konrad Szymanski told the private TVN24 television on Monday.
Kaczynski has hinted ongoing parliamentary and criminal investigations could lead to Tusk facing charges over an investment scam in which thousands of people lost money while he was prime minister.
A new probe has also been launched into the 2010 plane crash in Russia. Tusk has accused the PiS and Kaczynski of trying to exploit the tragedy for political reasons; his party, the PO, says the government wants to turn the case into a show trial.
PiS remains popular in Poland despite mounting accusations at home and abroad of authoritarian tendencies in its push to increase control over state institutions.
It has benefited from the lack of a charismatic leader of the centrist opposition since Tusk's departure to Brussels in 2014.
"Kaczynski remembers that when Donald Tusk was in Poland he was regularly losing all elections," said Malgorzata Kidawa-Blonska, deputy speaker of parliament and a member of the PO party.
"He is ready to blame Tusk for everything."
(Writing and additional reporting by Justyna Pawlak; editing by Mark Trevelyan)