Sen. Marco Rubio (R-FL) has joined the top tier of contenders to become Donald Trump’s running mate, but one Republican warned that he would provide very poor protection against impeachment. Trump once mocked the Florida Republican as “Little Marco,” most infamously during an exchange over their relative penis sizes at a GOP debate, but now Rubio is aggressively pushing his way onto the shortlist for 2024 vice presidential candidate, reported The Daily Beast. “He’s pushing hard, don’t let anyone tell you otherwise,” said one source who attended a recent donor retreat at Mar-a-Lago. “This didn’…