The launcher will crash immediately upon starting up with the following error:

We were unable to initialize launcher. Launcher will now close Reason: [-103] Unknown.

The logs show the following:
...
2015-12-19 15:34:11,685 [FATAL] 1: ShellWindow [Launcher.MainWindow.HandleWindowLoaded:0] System.BadImageFormatException: Could not load file or assembly 'SteamLayerWrap.dll' or one of its dependencies. is not a valid Win32 application. (Exception from HRESULT: 0x800700C1)
File name: 'SteamLayerWrap.dll'

   at Launcher.ViewModels.LauncherViewModel.<ViewLoaded>d__85.MoveNext()
   at System.Runtime.CompilerServices.AsyncVoidMethodBuilder.Start[TStateMachine](TStateMachine& stateMachine)
   at Launcher.ViewModels.LauncherViewModel.ViewLoaded()
   at Launcher.MainWindow.HandleWindowLoaded(Object sender, RoutedEventArgs args)

... {F27634} {F27635}