Mitt Romney sought to use the coveted endorsement of Jeb Bush on Wednesday to amplify his call for Republicans to rally behind his candidacy and get on with the mission of ousting President Obama.

Mitt Romney

As Mr. Romney savored a decisive victory in the Illinois primary on Tuesday over Rick Santorum, he learned that Mr. Bush — whose family name and appeal to both conservatives and moderates makes him as much an embodiment of the Republican establishment as anyone — was declaring his support and urging Republican voters to follow him.