Aslaksen and Hovstad tell him they won't print the article. Hovstad won't dare, because the subscribers control the paper and the proposal would ruin the town. The mayor gives Hovstad an official statement he can print to quell any rumors. The doctor resolves to hold a public meeting, but Aslaksen tells him that he won't find an organization to give him a hall.
In the second act, we saw the mayor turn on Dr. Stockmann. When that happened, the doctor still felt confident because he had the People's Herald behind him. In the third act, we see Hovstad and Aslaksen turn against him. The mayor has an easy time convincing them to turn against Dr. Stockmann. It is no surprise that economic arguments and the lack of visible evidence can be used to change Hovstad's mind.
But Ibsen goes further and shows us that Hovstad is simply not a reliable character. We learn that his support of the doctor is partly motivated by his affection for Petra. He even betrays his friend Billing for the sake of getting closer to Petra. Even before the mayor arrives and speaks to Hovstad and Aslaksen, they are discussing how they can use the doctor for their various ends. From the beginning, Hovstad is eager to use the doctor as a way to stimulate some sort of political revolution. When the mayor brings his carefully crafted arguments to men whose integrity is already compromised, they are easily won over to his side.
While the mayor and the doctor remain consistent in their opinions throughout the play, the newspapermen's ideas change. The mayor and the doctor have clear motivations: The mayor wants to stay in power, whereas the doctor is concerned with morality and science but not with economics or politics. The newspapermen, on the other hand, have many motivations, and, therefore, they can't come to a clear conclusion. Hovstad is a leftist radical, but he also wants to keep the paper in business, and he is interested in Petra. Ibsen uses these characters to illustrate how difficult it is to have a clear opinion in modern society. Hovstad can't afford to have a dangerous opinion and is, therefore, helpless when the mayor or the doctor has the upper hand.
Mrs. Stockmann is committed to her husband, but she is also committed to her family. When the doctor endangers the rest of his family by throwing away his job, she doesn't know what to do. She feels that Hovstad is fooling the doctor, and when Hovstad and all the other men turn on her husband, she feels that her husband has been led into a trap. It appears to her that the doctor has consistently tried to do what is best and has been somehow led into a very dangerous position by these men.
A few miscellaneous things should be explained. The mention of "Governor Stensgard" by Aslaksen is an allusion to Ibsen's early play, The League of Youth, in which Stensgard was a central character. Aslaksen was also a minor character in that play.