That's about as low as Harper will go. The 30% makes up hard-core Conservatives who will vote for the party no matter what.
But their influence doesn't stop there. When the PC and Reform parties united under the Conservative banner in 2004, the new party came to represent the 30%'s hard-core values. Moderate conservatives ended up marginalized, many forced to vote for the Liberal party.
What's worse is that the 30% that controls the Conservative party now controls the entire country. In 2011, it managed to win 40% of the vote and 54% of the seats, giving it 100% of the power.