WASHINGTON  With a fresh strategy team in place, the presidential campaign of Senator Hillary Rodham Clinton sought Monday to reassure supporters, contributors and Democratic delegates that her candidacy would withstand and be rejuvenated by the second leadership shakeup in two months.

Geoff Garin, a Democratic pollster, and Howard Wolfson, a longtime adviser to Mrs. Clinton, formally began their duties coordinating the campaign’s strategic message, replacing her chief strategist, Mark Penn. They worked feverishly  behind the scenes and through public channels  to convey that Mrs. Clinton’s efforts to win her party’s presidential nomination had not let up despite turmoil surrounding Mr. Penn’s departure.

Mr. Penn, a leading adviser to Bill and Hillary Clinton since 1996, relinquished his role as chief campaign strategist on Sunday after apologizing for holding talks with officials from the Colombian government about a bilateral trade treaty with the United States that Mrs. Clinton opposes. He met with the Colombians in his role as chief executive of Burson-Marsteller, a global public relations firm. Mr. Penn’s departure followed months of infighting between him and other Clinton aides.

The refurbished Clinton team faced challenges on Monday on two critical fronts: trying to contain any fallout from union members and other blue-collar workers who are essential to her success, and seeking to persuade key supporters and donors that Mr. Penn’s removal could breathe new energy into the campaign.