How to efficiently update conditional set of columns in large dataframe

Question

Given a large pandas data frame with columns Column_1 ... Column_n and a threshold X. What is an efficient way to set all subsequent columns to X once X is breached in each row. I.e. let's say we have threshold 1 and data frame the original dataframe is as in the link:

then the updated dataframe should be as in the second link:

Many thanks in advance!