Why didn't Dumbledore try to convince Slughorn a year earlier?

Question

Before Harry's fifth year at Hogwarts, Dumbledore has trouble finding anyone for the DADA job, and so Fudge gives him Umbridge. He must've known why Fudge wanted Umbridge there, and he must've known also that it wouldn't work out too well for him. The next year, he hires Slughorn as Potions teacher and Snape as DADA, which worked out fine. Except the part where

Snape killed him at the end of the year, but he wanted that to happen.

So why couldn't he have hired Slughorn a year earlier? It would've made life much less depressing for all of us.

Answer 1

A couple of reasons spring to mind:

• Slughorn would only have taken the Potions position, which leaves Snape to fill the DADA role. That would be a difficult decision.

  Two reasons for that:

  1. Snape is valuable to the Order of the Phoenix. He doesn’t want to risk losing him to the DADA curse.

  2. Dumbledore’s judgement is already in question for musing Voldemort’s return, and his defence of Snape was always controversial. Claiming that Voldemort has returned, and then appointing an ex-Death Eater to teach DADA, will raise a few eyebrows.

  Dumbledore has enough hassle already without adding these problems to his plate.

• He may not have had a choice in Umbridge’s employment.

  The official position is that the Ministry would only appoint a teacher if Dumbledore was unable to find a suitable alternative. The truth could be quite different.

  I think there’s a good chance that Umbridge was forced on Dumbledore. If so, he doesn’t have to reshuffle his other staff, there’s no hole in Potions, and hiring Slughorn is unnecessary. It’s the sort of thing Fudge would do, and Dumbledore may not have the political capital to resist.

  (Keeping Umbridge close may also be strategically useful. She may be annoying and dangerous at Hogwarts, but at least he can keep an eye on her. Keep your friends close, etc.)

• Slughorn’s key value to Dumbledore is for horcrux memories. This would be of questionable utility in Order of the Phoenix.

  Two reasons for this:

  1. It’s not clear whether Dumbledore is even aware of horcruxes at this point. If he isn’t, then there’s much less reason to re-hire Slughorn.

  2. In Order of the Phoenix, he’s worried that Voldemort might have access to Harry’s mind (hence the Occlumency lessons). Getting Harry to probe Slughorn for horcruxes while Voldemort is watching is very risky.

  Both of these problems are resolved by the start of Harry’s sixth year.

• By Half-Blood Prince, Slughorn is worn down by a year on the run.

  When he sees Harry and Dumbledore, he explains that he’s been on the move since the previous summer:

  Slughorn eyed Dumbledore balefully for a moment, then muttered, “I haven’t given them the chance. I’ve been on the move for a year. Never stay in one place more than a week. Move from Muggle house to Muggle house.”

  — Half-Blood Prince, chapter 4 (Horace Slughorn)

  It’s quite possible that Dumbledore thought he would be unable to recruit Slughorn when he’d only just gone into hiding. It’s likely that he was keeping tabs on Slughorn, and would know he’d just tried to hide. Trying and failing to get him once might make it harder to recruit him in future.

• He doesn’t want to risk Snape’s life with the DADA curse.

  As stated above, if he hired Slughorn for Potions then Snape goes to DADA.

  As a double agent, Snape is of great utility to the Order. But previous DADA teachers have often been incapacitated (Quirrell, Lockhart); it would be foolhardy to put such a valuable asset at risk, especially when he has other options.

Answer 2

Because there was no reason for him to hire Slughorn in year 5:

• He didn't want Slughorn dead, so he would not hire him for DADA
• He also didn't want to lose Snape, so he wouldn't move Snape to DADA (this needing a Potions Master).

So... we are STILL stuck with Umbridge for Year 5, and nothing useful for Slughorn to do.

Also, the whole point of Year 5 was to make life more depressing for "us". That's part of the craft of storytelling.

P.S. While largely tangential to the main question, another possible reason is that Dumbledore wouldn't have any chance to convince Slughorn in Year 5 - and he is smart enough to know that. Harry wasn't a positive celebrity yet (pre-MoM battle and Voldemort reappeairing) so Slughorn had no need to "collect" him; and Slughorn wasn't in need of protection from Death Eaters yet. (h/t/ Himarm)

Answer 3

Some good reasons were given by the previous answers, but I think that a few more points may be raised.

1. Politics.

   Claiming that Voldemort returned place Dumbledore in a difficult political position. Letting the ministry choose one of his teachers would appear as an attempt to avoid a direct confrontation (that he would probably lose). Complying with the ministry would soothe the fear that Fudge & co. were trying to spread.

2. He did not yet have the idea

   Dumbledore was very clever, and was trying to plan several years in advance. However, it may happen that he did not yet have the idea of using Harry as a tool to convince Slughorn to give the real memory. He had other pressing matter at hand, and maybe the idea wasn't there yet.

3. Relation with Harry.

   That year, if you recall, Dumbledore wanted to separate himself from Harry. And without close relation, he could not set Harry to the task and in particular impress on him the importance of the memory. Even the year afterwards, it was only after he started to show some of the memories that Dumbledore set Harry to the task or retrieving that memory. Which means some extra research.