WASHINGTON -- The Republican establishment started to coalesce around Mitt Romney in earnest yesterday, 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 found himself having to defend his conservative credentials anew after one of his own top advisers, Eric Fehrnstrom, remarked that "everything changes" for the fall campaign. "It's almost like an Etch A Sketch," he said. "You can kind of shake it up and we start all over again."

The remark 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.

"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.

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 Wednesday he publicly backed Romeny. "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 his lead after sitting on the sidelines.

But the Etch A Sketch remark threatened to dog Romney. 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."

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