WASHINGTON (CBSNewYork/AP) — The war of words between Republican presidential candidate Donald Trump and Mitt Romney continued Thursday, a day after Romney said he thinks there’s a “bombshell” in Trump’s tax returns.

Trump took to Twitter, calling Romney one of the “dumbest and worst candidates” in Republican history.

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“Mitt Romney, who was one of the dumbest and worst candidates in the history of Republican politics, is now pushing me on tax returns,” Trump tweeted. “Dope!”

He also posted a photo of himself sitting next to a large stack of papers that he said showed him signing a recent tax return.

“Just for your info, tax returns have 0 to do w/someone’s net worth. I have already filed my financial statements w/FEC. They are great!” he said in another tweet.

Romney responded to Trump’s Twitter rant with his own post, saying, “Methinks the Donald doth protest too much. Show voters your back taxes” with the hashtag #WhatIsHeHiding.

The 2012 Republican presidential nominee said on Fox News Wednesday that the contents of Trump’s tax returns are the reason the billionaire developer has not released them.

“Frankly, I think we have good reason to believe that there’s a bombshell in Donald Trump’s taxes,” he said. “Every time he’s asked about his taxes, he dodges and delays and says, ‘well, we’re working on it.'”

Trump said he’ll release his returns when he’s ready.

“My returns are extremely complex and I’ll make a determination at the right time,” Trump told CNN. “I’m in no rush to do it. Nobody has been bringing it up except for Mitt Romney.”

But Romney isn’t the only one pushing for the release. Ted Cruz chimed in at a presidential candidates forum hosted by The Kelly File on Fox News.

“I do think Mitt has a good point that the voters are entitled to know before they vote, because you better believe the Democrats, if there’s anything in there, the Democrats will go to town on this,” he said.

Romney is also calling on Cruz and Marco Rubio to release their tax returns.

“They are just not very exotic, but we will release them,” Rubio said.

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“Look, the nice thing is I haven’t made enough money. My tax returns aren’t that interesting,” Cruz said.

The former Massachusetts governor came under intense scrutiny in 2012 over his own tax filings.

Romney also said he believes Trump has the clearest path to the Republican nomination and that there is “a slimmer and slimmer opening” for his rivals unless the field narrows.

In another Tweet Thursday, Trump said “I’m going to do what Mitt Romney was totally unable to do- WIN!”

As CBS2’s Dick Brennan reported, the other candidates jumped at the chance to tout their transparency.

“Very glad to release tax returns,” John Kasich said.

As was Ben Carson.

“Got nothing to hide, not a problem,” he said.

Meanwhile, Rubio and Cruz will get to take their shots at Trump in person at a GOP debate Thursday night in Houston.

In upcoming primaries, Trump will be battling candidates in their home states. He leads Rubio by a big margin in Florida, trails Cruz in Texas and leads Kasich in Ohio.

Texas is the biggest prize on Super Tuesday with 155 delegates at stake.

In the meantime, Trump was taking flak from another front over his bid to build a border wall and make Mexico pay for it.

“I’m not gonna pay for that (expletive) wall. He should pay for it. He’s got the money,” former Mexican President Vincente Fox said, “Democracy cannot support crazy people who do not know what’s going on in the world.”

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