YUROP

The only way the conservatives get the funding for increased arms manufacturing is by disabling/changing something about the debt ceiling.

Debt ceiling is in the basic law (constitution), which requires a 2/3 majority to be altered.

Linke are against the debt ceiling in general, but not if it's only disabled for military spending while still preventing investments in public infrastructure. I think with a bit of diplomacy and concessions in the wording, Linke can be persuaded here.

Edit: Or Merz can just say he doesn't want to change anything about the debt brake, OK. Saves him from negotiating anything I guess. Maybe the billions he needs will just fall out of the sky then.

Edit2: Quite the heel-turn. So they just announced that SPD and CDU want to reform the debt brake. They plan to reach the 2/3rds needed by... rushing it through before the new parliament forms. This means they do not need to negotiate with Die Linke, but with the Greens. Quick reminder that the last government, which included the greens, collapsed because CDU wouldn't help reform the debt brake. Either be forever known as spineless suckers (like the SPD) or be the ones blamed for the fall of Ukraine, no good options for the greens here.