Except that's not what you originally said:
The party ruling at that time was PiS, not Tusk, as you yourself noted by saying here Tusk was in opposition and thus not President.
Is that why almost 50% of the Sejm didn't vote on the resolution declaring Russia a state sponsor of terror?
Well "Historyczku" I will explain to you as simply as possible so that you understand how badly you have twisted what happened.
The SLD (Democratic Left Alliance), i.e. post-communists pretending to be social democrats, ruled until October 2005. As a result of being a typical left-wing bunch, they eventually aborted the 2005 elections for both president and parliament.
In both, PiS won, but was immediately followed by PO. PiS itself was and is known for its anti-Russianism. The first Western politician to arrive in Georgia during the 2008 war was PiS-appointed president Lech Kaczynski, and Kaczynski himself was a de facto foreign policy rival to the foreign minister.
PO, which was already in power at the time, less willing to go anti-Russian and spoke empty platitudes about peace talks, which was an important signal of what would happen later.
But coming back, after winning the elections, PiS had to look for a coalition partner because it did not have a direct majority. Originally, it was supposed to be PO, but PO torpedoed the plans just before election day and Tusk spoke out strongly against it.
As a result, PiS was forced to look for new coalition partners and, in practice, for two years was more preoccupied with holding on to power than with real action, while PO, together with most of the opposition, rode roughshod over the ruling party. Eventually there were early elections in 2007 in which PO went to many undignified lengths in its election propaganda. Ultimately, these elections were lost by PiS and it went into opposition with only the president.
PO quickly and effectively built a governing coalition with the PSL and then, when it won, it began the so-called "cotton-picking", i.e. the elimination of PiS from the normal political game, most simply compared to what the Democrats are trying to do with Trump and the MAGA Republicans, only more brazenly.
When the US-Russia reset happened it was PO, not PiS, that was the party acting pro-Russian, they were so pro-Russian that they agreed to an eminently unfavourable deal for Poland with Gazprom that it was only the actions of the EU that turned the issue on its head and gave Poland a much better deal.
Until the death of President Kaczyński, he was in conflict with the government because, like PiS, he was anti-Russian and looked unfavourably on Tusk's and his party's affinity with the Russians.
And most importantly, in Poland the president is not as important as for example in France or the USA, despite a constitution that tries to make him the centre, de facto power is held by an unelected prime minister answering only to his coalition in the Sejm. That the president was from PiS is one thing, that the foreign minister was from Po is another. And they both got in each other's way, Kaczyński going against Russia, Sikorski going with Russia.
And the PO's attitude towards the ex-president is well illustrated by a malicious joke called "Kaczka* Smolensk-style" uttered by the cultural background of the ruling party.
*The name in question is Kaczynski, which can be maliciously shortened to Kaczor which means Duck.
