Donald Trump is now focused on attacking Mitt Romney as the GOP's failed 2012 nominee is waging an anti-Trump campaign. It's the latest twist in the bizarre 2016 presidential race.

Romney plans to deliver an address Thursday calling for a unified effort by establishment Republicans to stop Trump's takeover of the GOP.

Trump responded with a video that questions Romney's conservative credentials and flip flops on immigration, abortion rights, Obamacare, global warming and the federal economic stimulus efforts.

Looks like two-time failed candidate Mitt Romney is going to be telling Republicans how to get elected. Not a good messenger!

— Donald J. Trump (@realDonaldTrump) March 3, 2016

As Republican leaders show increasing signs of plotting against the frontrunner Trump, he is making it clear they would pay a price for it.

Because of me, the Republican Party has taken in millions of new voters, a record. If they are not careful, they will all leave. Sad!

-- Donald J. Trump (@realDonaldTrump) March 3, 2016