WARSAW, Poland (AP) — Polish opposition leader Donald Tusk is facing an uphill battle to win new hearts in his efforts to unseat the nationalist conservative government in Poland’s upcoming parliamentary election.

The ex-prime minister and former European Union leader returned to Polish politics several years ago, seeking to breathe new life into his languishing party and win back power — and reverse what many view as a degradation of fundamental rights and ties with European partners under the governing populist Law and Justice party.

Tusk, 66, is hoping a major rally that he organized for Sunday will energize his supporters.

But he faces many obstacles, including divisions among his opposition ranks and, even more importantly, powerful government forces that depict him as disloyal to the nation.

Shaping the campaign is a long and bitter personal rivalry between Tusk and Law and Justice chief Jaroslaw Kaczynski, who is the country’s 74-year-old de facto leader. Kaczynski, other government figures and state media repeatedly allege that Tusk’s time as prime minister from 2007 to 2014 was harmful to Poland.

They point to the good terms he was on with then-German Chancellor Angela Merkel to make unproven allegations that he represented the interests of Germany, a neighboring country that brutally occupied Poland during World War II. They also accuse him of abandoning Poland when he went to Brussels in 2014 to become European Council president, a top EU post.

“Herr Donald, you left Poland to serve German interests in Brussels, for big money. … I gave up a high salary in order to serve Poland,” Prime Minister Mateusz Morawiecki, a former banker, recently tweeted after Tusk questioned whether he was hiding his wealth.

Tusk has denied being partisan to Germany and laughs off the allegations.

Tusk’s “March of a Million Hearts” on Sunday comes two weeks before the Oct. 15 vote. His electoral alliance, the Civic Coalition, trails a few percentage points behind Law and Justice in opinion polls.

The march, the coalition’s biggest campaign event, was inspired by the huge success of a similar march on June 4 that drew hundreds of thousands of opposition supporters from across Poland.

One of Tusk’s greatest challenges is convincing supporters that the incumbent party can be defeated despite having consolidated huge power.

“On June 4, you gave Poland hope, so I am asking you now: On Oct. 1, let’s give not just hope, but the full belief in victory, in our success in removing these evil people from power,” Tusk said when announcing Sunday’s march.

Tusk has been pushing back against the populist government’s attempts to cast him as unpatriotic. His campaign symbol is a heart in the national colors of white and red to show that “we all have Poland in our hearts.”

The June 4 march saw a huge outpouring of solidarity because it was held after Law and Justice passed contentious legislation establishing a state commission for investigating Russian influence in Poland. The law was seen as the governing party’s way of targeting Tusk and removing him from public life. Instead, it rallied support for Tusk and boosted his electoral chances.

Opposition groups put aside their differences and marched with Tusk then. But this time, an opposition alliance called the Third Way — a coalition of the centrist Poland 2050 party and agrarian Polish People’s Party (PSL) — won’t take part.

The Third Way participated then because the Russian influence commission “made it very clear that the ruling team, using uncivilized methods, wants to get at the leader of the biggest opposition party,” Sen. Jan Filip Libicki, of PSL, told The Associated Press. “There was a reason for this extraordinary mobilization.”

Libicki says there is no such pressing matter now.

These divisions complicate Tusk’s attempts to return to power. His electoral alliance includes his Civic Platform party and three other small parties. However, apart from the Third Way, there is also the Left party in the opposition camp and it’s competing for younger voters against the far-right Confederation party. The party has been growing in popularity, especially among young men fed up with the political parties that have dominated Poland for most of the post-Communist era.

Rafal Chwedoruk, a political scientist with the University of Warsaw, says Tusk’s coalition, the Left and the Third Way together seem poised to get a majority of the votes, judging by opinion polls. But they haven’t worked out a joint electoral strategy.

Some analysts see the disunity in the opposition as partly Tusk’s fault.

Tusk is a charismatic leader with long political experience at home and internationally. But he also has a reputation for being domineering toward others in his party, and that has led some to leave and join other groups, like Libicki did in 2018.

Tusk recently moved his centrist alliance to the left, courting women and younger voters. Civic Platform has traditionally taken a fairly conservative position on abortion. But after a near-total ban was imposed under Law and Justice, Tusk vowed to liberalize the abortion law and has threatened to ban party members who criticize his plan from running in the election.

Lawmaker Boguslaw Sonik quit Tusk’s party this year amid disagreements on abortion and the general drift to the left, and is now unaffiliated.

“A party cannot be run in a military style,” he said on commercial radio station RMF FM. “These are matters of conscience.”