Gov. Bob McDonnell (Cliff Owen/AP)

Gov. Bob McDonnell, chairman of the Republican Governors Association, will appear with Walker at an event Tuesday, according to his office, though details have not been released.

Attorney General Ken Cuccinelli asked supporters to donate to Walker’s campaign in what he called the “second most important election in America in 2012.’’

“June 5th will be a clash of political forces of titanic proportions that will affect how (and whether) others in politics will meaningfully take on our biggest challenges, all of which entail taming and reining in government,’’ Cuccinelli wrote.

Recent polls show Walker pulling ahead of Milwaukee Mayor Tom Barrett (D).