Apparently a lot, especially in this year’s Democratic race.

Sen. Hillary Clinton has altered hers frequently depending on what her staff believes its message should be on that particular day. In recent weeks, an embattled Sen. Barack Obama has followed suit, albeit more subtly.

Take a look at the use of the campaign signs on the podium when Barack Obama is giving a speech. For the longest time, “Change We Can Believe In” sufficed and resonated - but front-runners inevitably are subject to scrutiny.

Therefore, “Judgment to Lead” became the theme from Team Obama early last month, around the time of the Iraq war’s fifth birthday and amid doubts that the Illinois Senator is ready to assume the role of Commander-in-Chief.

Echoing that theme later in March (when he was also trying to move away from criticism over remarks made by his ex-pastor, Rev. Jeremiah Wright), Obama opted for the even more overt “End the Iraq War Now / Invest at Home.”

It’s the essence of political strategy, and as the Democratic race intensifies in April, we can expect several more subtle alterations to the candidates’ messages.