Former President Donald Trump criticized for controversial immigration speech.

Trump's comments about immigrants 'poisoning the blood' of America likened to Adolf Hitler's rhetoric.

Trump denies being inspired by Hitler, claims he was discussing negative impact of illegal immigration.

President Biden and other critics condemn Trump's comments as racist and xenophobic.

Despite controversy, Trump leads in polls among likely Republican voters.

Reports of Trump's past interest in Hitler's speeches fuel skepticism about his denials.