Republicans are already attempting to block House Democrats from investigating a meeting former President Donald Trump held with oil and gas executives that critics have called an act of “undisguised corruption,” a new letter shows. The investigation would potentially look into Trump’s reported demand, made at a Mar-a-Lago dinner in April, for $1 billion in campaign funding in exchange for environmental regulation cuts should he regain the White House. Senate Democrats launched an investigation into the April 11 dinner, and promises reportedly made to top executives, earlier Thursday. Want mor…