President Obama and British Prime Minister David Cameron kick off two days of diplomacy this morning by pledging to work against repressive regimes in the Middle East -- by force if necessary.

In a sternly worded column in The Times of London, the two leaders liken the effort to free Arab people from authoritarianism to the Cold War and the fall of the Berlin Wall in the 1980s.

They liken their personal efforts to two leaders who came before them: Ronald Reagan and Margaret Thatcher.

"We will stand with those who want to bring light into dark, support those who seek freedom in place of repression, aid those laying the building blocks of democracy," they wrote.

"We will not stand by as their aspirations get crushed in a hail of bombs, bullets and mortar fire. We are reluctant to use force, but when our interests and values come together, we know that we have a responsibility to act."