Watching the occasional TV program, I often feel sorry for guests trapped on talk shows who haven't learned to hold their own long enough to state their views. Others interrupt them to the point that it appears someone has hit their "mute" button and shut them down. On a panel in a 7-minute time slot, the panelist can disappear after the first go-around unless the moderator saves them by tossing a question to them by name.
To hold your own and keep this from happening to you, set yourself up to hold the floor from the outset. In a meeting with someone who habitually interrupts, speak in a firm voice and state your framework to signal others where you intend to go: "Let me point out three reasons I think we should reconsider funding this project..." If the interrupter butts in after reason one, continue in a firm voice, "Please let me finish with my other two reasons..." and continue.
Stake your claim to hold the floor. Refuse to be rudely interrupted.