Why the Ukraine mess is leading to anxiety in Pence's world?

Because Trump sent Pence to the Ukrainian president's inauguration to tell them he was removing the 391 million military package from them. By doing this he put Pence in the middle of the present scandal and because of this not only Trump but Pence could also be removed from office. In this case Nancy Pelosi would become President and become the first female president in the U.S. by default as Speaker of the House of Representatives. We have very firm "chain of command" rules here in the U.S. that were set up because of wartimes in the past and nuclear weapons taking out the president and Vice President in some future presidency. So, if both Trump and Pence are removed from office Nancy Pelosi would "through chain of command" become the first female President of the U.S. and she would serve out the Trump-Pence term in office.