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Given the following post, respond as if you're commenting on Reddit:
human
[Harry Potter] In Book Five, when Harry serves detention with Prof. Umbridge, she has him use a special quill.

This special quill wrote in Harry's blood and caused scarring to Harry's hand. This is a form of corporal punishment, which is not allowed at Hogwarts. However, Harry decides not to tell Dumbledore or any other staff member.

What would have been the fallout if Harry had gone to Dumbledore right away to show him what Umbridge was doing?
gpt
Dumbledore tolerated Umbridge due to the difficult political situation he was in, but showed willingness to abandon political expedience to physically protect students, such as when he cursed Umbridge in front of witnesses to stop her shaking Marietta. 

As well as that, discovering a magical torture device in her possession could have been a potential advantage for Dumbledore: even with the press so heavily against him, Dumbledore has enough leverage to publicise the Ministry using probably-illegal cursed items on children. 

All told, if Dumbledore had known, he would probably have gone full meddle-not on Umbridge and hauled her before the Wizengamot. There's no particular indication that Fudge would have been willing to risk his already-precarious position to defend her. It wouldn't have been enough to restore Dumbledore, but it would have got Umbridge removed from Hogwarts and damaged the Ministry's position. 

Even if it didn't work out like that, Dumbledore would *definitely* have destroyed the cursed quill and kept a much closer eye on Umbridge.