People call politicians names all the time and politicians and their supporters just take it in stride. Why did equating President Wilson to the German Kaiser in the "Kaiser Wilson" poster enrage the President and the crowds that assaulted the suffragists?

It enraged the crowd and the president because the country was at war with Germany and equating him to the Kaiser was an insult due to the atrocious actions that had been committed by him.

Explanation:

During the women's suffrage movement, suffragists considered that US president Woodrow Wilson was deceitful and a fraud. The reason is that he was fighting for democracy abroad while he and his supporters were forbidding the right to vote to women, who were American citizens. Thus, he was acting in opposition to the ideal democracy in his own country.