The campaign of Gary Johnson, the Libertarian Party's presidential nominee, sent letters to major polling firms this week asking them to include him in any surveys they conduct as a prelude to trying to earn his way into the presidential debates this fall. The Commission on Presidential Debates, the semi-official group that hosts the quadrennial showdowns, relies on polling performance as a chief measure of whether they invite third-party candidates to participate. The other requirement is that a candidate appear on enough states' ballots to be able to earn enough electoral votes to become president. Mr. Johnson has already met that through the strength of the Libertarian Party's operation. But the polling requirement is trickier. Many polls simply ask about a head-to-head match-up between President Obama and presumptive Republican nominee Mitt Romney, meaning Mr. Johnson is left out. In the campaign letter, his vice presidential nominee, Jim Gray, said Mr. Johnson is polling in the significant single digits in some states, which he said shows the Libertarian ticket "has the backing to affect the election's outcome."