WASHINGTON >> The Republican establishment started to coalesce around Mitt Romney in earnest today, with Jeb Bush and other leading Republicans pressuring Rick Santorum to leave the race after a thumping in the Illinois primary. 

But, on what should have been a triumphant day, Romney also found himself having to defend his conservative credentials anew after one of his own top advisers quipped that the GOP front-runner’s policy positions are “almost like an Etch A Sketch” in that they could be shaken away and redrawn.

“The issues I’m running on will be exactly the same,” the former Massachusetts governor said in Arbutus, Md., as Republicans and Democrats alike mocked him. “I’m running as a conservative Republican. I was a conservative governor. I will be running as a conservative Republican nominee — hopefully, nominee at that point. The policies and the positions are the same.” 

The remark earlier in the day by adviser Eric Fehrnstrom fueled criticism that Romney molds his principles to fit with political goals. Democrats pounced, and by day’s end his GOP opponents were waving the draw, shake and erase toys at campaign events in Louisiana.

It all nearly overshadowed the endorsement from Bush, the son of one president and the brother of another. He had stayed out of the race for months, and some party elders publicly had urged him to become a candidate as Romney struggled to close the deal with the conservative base of the party.

Bush refused, and today he made his preference in the race known after Romney’s double-digit Illinois victory.

“Now is the time for Republicans to unite behind Gov. Romney and take our message of fiscal conservatism and job creation to all voters this fall,” Bush said in a written statement. He congratulated the other Republican candidates “for a hard-fought, thoughtful debate and primary season.”

His backing comes amid fresh signs that big GOP donors and other party figures will follow Bush’s lead after sitting on the sidelines for much of the primary season. Romney is on pace to win the nomination in June. He has 563 delegates in the overall count maintained by The Associated Press, out of 1,144 needed to win the party nod. Santorum has 263 delegates, Newt Gingrich 135 and Ron Paul 50.

Hours after Bush weighed in, Bob Dole, the former Senate majority leader and a longtime Romney supporter, suggested that Santorum must decide soon whether to stay in or surrender his bid for the nomination. 

“Rick, I think, he’s got a real problem,” Dole, who became the GOP nominee in 1996 on his third try, told The Associated Press in a telephone interview. “It’s getting close to the point where he’s got to take a hard look at it.”  

At the same time, campaign finance reports released Tuesday showed that big donors to a GOP political organization founded by political strategist Karl Rove have boosted their financial support for Romney in recent weeks.

Bush’s support came as a surprise to the Romney campaign. The former Florida governor personally contacted Romney this morning to say he planned to make the endorsement.

Romney made one quick public appearance in Maryland today ahead of the April 3 primary there. He planned to spend much of Thursday personally courting members of Congress and other officials in Washington.

But the Etch A Sketch remark threatened to dog him.

It happened early today on CNN when Fehrnstrom was asked if the extended primary fight “might force the governor to tack so far to the right it would hurt him with moderate voters in the general election.”

Fehrnstrom responded: “I think you hit a reset button for the fall campaign. Everything changes. It’s almost like an Etch A Sketch. You can kind of shake it up and restart all over again.” The aide didn’t back away from the comment when asked to clarify it. He said only that the general election is “a different race, with different candidates, and the main issue now becomes” exclusively President Barack Obama.

It didn’t take long for the Democratic National Committee and Romney’s Republican rivals to seize on the remark.

In Louisiana, Santorum brandished an Etch A Sketch and told voters he is a candidate who stands “firmly on the rocks of freedom, not on the sands of an Etch A Sketch toy.”

Gingrich stood on stage elsewhere in the state and explained to his audience just what the toys were. “Gov. Romney’s staff, they don’t even have the decency to wait until they get the nomination to explain to us how they’ll sell us out,” he said. “I think having an Etch A Sketch as your campaign model raises every doubt about where we’re going.”

Louisiana holds its primary Saturday. Santorum is favored in the state, though Romney’s allies are airing TV ads there even though the South has proven less hospitable to Romney.

Beyond Saturday, polls show Romney has the advantage heading toward Maryland’s April 3 primary. 

For his part, Obama today headed to Nevada, New Mexico and Oklahoma on a trip aimed at answering critics of his energy policies, sure to be a key issue in the fall campaign. His first stop was a plant in Nevada that uses solar panels to power homes, part of an effort to highlight his programs to expand renewable energy sources.

The president’s GOP critics poked back at Obama before Air Force One even took off.

Gingrich issued a statement saying Obama was answering a real-world problem with a “solution that is totally disconnected from the practical realities of the world and has little chance of success.” Crossroads GPS, the nonprofit arm of a Republican super PAC, launched an ad on TV stations in the areas on Obama’s itinerary and on national cable channels faulting the president for “bad energy policies” that are driving up gasoline prices.