WASHINGTON  Senator John McCain’s presidential campaign is in a troubled stretch, hindered by resignations of staff members, a lagging effort to build a national campaign organization and questions over whether he has taken full advantage of Democratic turmoil to present a case for his candidacy, Republicans say.

In interviews, some party leaders said they were worried about signs of disorder in his campaign, and if the focus in the last several weeks on the prominent role of lobbyists in Mr. McCain’s inner circle might undercut the heart of his general election message: that he is a reformer taking on special interests in Washington.

“The core image of John McCain is as a reformer in Washington  and the more dominant the story is about the lobbying teams around him, the more you put that into question,” said Terry Nelson, who was Mr. McCain’s campaign manager until he left in a shake-up last fall. “If the Obama campaign can truly change him from being seen as a reformer to just being another Washington politician, it could be very damaging over the course of the campaign.”

The ousters of some of the staff members came after Mr. McCain imposed a new policy that active lobbyists would not be allowed to hold paying jobs in the campaign.