Part of the point of having portfolio management processes and, in particular, decision making criteria is to ensure that individual projects are not:

• De-railed or continued based on irrational/inconsistent decision making
• Delayed waiting for senior executives to become available to make decisions

However, one really good organisation and set of portfolios was damaged by an R&D manager who would not and could not let go of the reins.  He consistently interfered in decisions and seriously under-mined the process.  You need to lead from the top and if the senior team won’t play the game then they can’t expect anyone else to take them seriously.