In 1853, Commodore Matthew Perry visited Japan with the intent of forcing Japan to open up to trade with Western countries. His visit helped trigger a series of events that ultimately led to the downfall of the Tokugawa Shogunate and its replacement with the Empire of Japan in 1868. How responsible was Matthew Perry's visit to Japan and its aftermath for the downfall of the Tokugawa Shogunate? Was the shogunate already doomed to collapse even before Matthew Perry arrived? If so, why? How much longer would the shogunate have lasted had Matthew Perry not visited and forced Japan to open up to trade?
It really depends what you mean by trigger. The Shogunate was straining under a lot of pressures by the 1850s and already dealing with a number of rebellions. One major cause for the strain was a shift in the economy similar to what was going on in the rest of the world. In the 1800s, Japan was becoming increasingly urban and the samurai class(rulers under the Shogunate) was having difficulty keeping up with the economic growth. There were a series of bad harvests in the 1830s and the efforts of the Shogunate to maintain economic control in the 1840s were very conservative and disrupted trade. Overall, the social order of the time was very fragile. The samurai felt unstable in their positions of power and those involved in trade chafed at government control.
That said, Perry's arrival and success at opening up trade did serve as a catalyst and provoked a traditionalist samurai rebellion. While the Shogunate was able to put it down, it opened the floodgates for other rebellions and eventually the rise of the Meiji government. Their fragile control eventually broke.
We can't really say how much longer the Shogunate would have lasted. It might have lasted until serious attempts at Russian expansion that would result in the Russo Japanese War, but it might have crumbled under it's own weight beforehand.
Source: Duus, Peter. 1998. Modern Japan. https://smile.amazon.com/Modern-Japan-Duus-Peter-Paperback/dp/B008YT09KA/ref=sr_1_2?crid=1E9C16JCHW0FN&dchild=1&keywords=peter+duus+modern+japan&qid=1615401952&sprefix=peter+duus%2Caps%2C168&sr=8-2