Alanna Durkin Richer ?and Calvin Woodward

VIRGINIA BEACH, Va.: Republicans are barreling toward Super Tuesday with another debate in the pipeline and Donald Trump’s opponents reaching for perhaps their last best chance to knock him off stride for the presidential nomination.

Expect a nasty turn, Trump warned, as if the roiling GOP race were anything but that already.

The New York billionaire predicted that the relative civility between Marco Rubio and himself would fall away in the frantic grasp for hundreds of convention delegates in the 11 states that hold Republican primaries Tuesday.

Even Ohio Gov. John Kasich, a trailing contender whose calling card has been a positive campaign, went sharply negative Wednesday in a campaign broadside against Rubio, the Florida senator who is soaking up Republican establishment support and thereby threatening to starve Kasich’s effort of its remaining oxygen.

Trump exercised bragging rights with trademark gusto after Nevada handed him his third straight victory the night before.

Relaxed on stage at Virginia’s Regent University, Trump fielded questions from Christian conservative figure Pat Robertson, ticking off Obama administration executive orders he wants to reverse as president and joking about his recent dustup with the pope.

He said earlier he might tone down his contentious rhetoric if he makes it to the White House — or not, since “right now it seems to be working pretty well.”

And what of Rubio?

“So far he’s been very nice and I think I’ve been very nice to him,” Trump said on NBC’s Today show. “We haven’t been in that mode yet but probably it’ll happen.” It can be presumed he meant attack mode.

Tax returns in spotlight

Also Wednesday, Trump hit back after Mitt Romney suggested that a “bombshell” is lurking in the tax returns Trump has so far refused to release.

Romney was the GOP nominee in 2012. Trump said on Twitter that “Mitt Romney, who totally blew an election that should have been won and whose tax returns made him look like a fool, is now playing tough guy.”

Romney said in an interview with Fox News that Trump’s foot-dragging on releasing his returns suggests he has something to hide.

Trump has said his accountants are working on his returns and that he’ll release them eventually.

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

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

On the Democratic side, Hillary Clinton scored the endorsement of Nevada’s Harry Reid, the party’s Senate leader, before a primary Saturday in South Carolina, where she looks strong. She prevailed in the Nevada Democratic caucuses, dulling rival Bernie Sanders’ drive and making Super Tuesday of crucial importance to him.

On Tuesday:

•?Republicans will award 595 delegates in 11 state races, with 1,237 delegates needed to clinch the nomination.

•?Democrats will award 865 delegates in 11 states and American Samoa, with 2,383 needed for the nomination.

The election calendar suggests that if Trump’s rivals don’t slow him by mid-March, they may not ever. Delegate totals so far: 82 for Trump, 17 for Ted Cruz, 16 for Rubio, six for Kasich and four for Ben Carson.

For Republicans, Nevada offered little evidence Republicans are ready to unite behind one strong alternative to Trump, who many in the party fear is too much of a loose cannon to win in November.

Mainstream Republicans who don’t like Trump are also in large measure cooling on Cruz. With Jeb Bush out of the race and time short, they have begun gravitating to Rubio, long a man of promise in the race but one who has yet to score a victory.

The Florida senator edged Cruz, a Texas senator, for second place in Nevada, and it’s clear his time is at hand — if he’s to have one.