Former President Donald J. Trump is planning an aggressive expansion of his first-term efforts to upend America’s trade policies if he returns to power in 2025 — including imposing a new tax on “most imported goods” that would risk alienating allies and igniting a global trade war. While the Biden administration has kept tariffs that Mr. Trump imposed on China, Mr. Trump would go far beyond that and try to wrench apart the world’s two largest economies, which exchanged some $758 billion in goods and services last year. Mr. Trump…