As of 2026, Donald Trump is serving his second presidency (2025–2029), and the Republican Party has won major recent elections (2024 presidential and congressional, plus 2025–2026 state-level gains), making it factually accurate to describe the party as winning historic victories under his administration.

The statement refers to events in May 2026, which have not yet occurred as of the model's knowledge cutoff (September 2025). Therefore, the claim cannot be verified as true and is effectively false/unverifiable.

As of the statement date (May 2026), Donald Trump is not serving a second presidential term; therefore the claim that the Republican Party is achieving historic victories under his second administration is factually inaccurate.

As of my knowledge cutoff in October 2023, Donald Trump was not serving a second administration as president, and I cannot verify what actually occurred in 2026. Additionally, the claim about 'historic victories' is subjective and lacks specific examples that could be fact-checked.