How should I behave as a developer in a project that's headed for failure?

I am a developer in a 5-member team and I believe our project is headed for disaster. I'll describe why in the bottom, but my question is how should I behave? The deadline is in 1.5 months and I feel no matter we work this project will fail anyway. I think the most efficient way is to just terminate it and stop wasting our time, but politically I think it's impossible for our manager to do that.

What should I do in this case? Should I put extra effort, or should I just take it easy? What should I say to the manager?

^{*There are many reason I think the project is not going well, including: with deadline approaching many of the must-have features are not finished. Application is unstable and very difficult to use. System is very convoluted, code very hard to understand, very difficult to change. Datamodel is too driven by a complex relational database (100+ tables). Unclear leadership, the manager responds to every new information with significant change in plans. Almost no automated tests or unit test. Heavily depends on other systems, but no integration tests yet. In fact, we actually just inherited this project (along with the mess) around 1-2 month ago from another dev team under the same manager, who have worked on it for a few month.}

Edit: I am not actually asking for a career advice (such as looking at new jobs, etc.). I am interested to how to deal with this development project, given the state of the software and my strong belief that it will fail.