Democrats preparing to vote in Tuesday’s California primary can mark their ballots with confidence, knowing that either candidate would make a strong nominee and, if elected, a groundbreaking leader and capable president. But just because the ballot features two strong candidates does not mean that it is difficult to choose between them. We urge voters to make the most of this historic moment by choosing the Democrat most focused on steering the nation toward constructive change: We strongly endorse Barack Obama.

The U.S. senator from Illinois distinguishes himself as an inspiring leader who cuts through typical internecine campaign bickering and appeals to Americans long weary of divisive and destructive politics. He electrifies young voters, not because he is young but because he embodies the desire to move to the next chapter of the American story. He brings with him deep knowledge of foreign relations and of this nation’s particular struggles with identity and opportunity. His flair for expression, both in print and on the stump, too easily leads observers to forget that Obama is a man not just of style but of substance. He’s a thoughtful student of the Constitution and an experienced lawmaker in his home state and, for the last three years, in the Senate.

On policy, Obama and his rival Democratic candidate, Sen. Hillary Rodham Clinton of New York, are a hairsbreadth apart. Both vow to pull troops from Iraq. Both are committed to healthcare reform. Both offer candid critiques of the failed George W. Bush presidency, its blustering adventurism, its alienating stance toward other countries and its cavalier disregard for sacred American values such as individual liberty and due process of law.

With two candidates so closely aligned on the issues, we look to their abilities and potential as leaders, and their record of action in service of their stated ideals.Clinton is an accomplished public servant whose election would provide familiarity and, most important, competence in the White House, when for seven years it has been lacking. But experience has value only if it is accompanied by courage and leads to judgment.

Nowhere was that judgment more needed than in 2003, when Congress was called upon to accept or reject the disastrous Iraq invasion. Clinton faced a test and failed, joining the stampede as Congress voted to authorize war. At last week’s debate and in previous such sessions, Clinton blamed Bush for abusing the authority she helped to give him, and she has made much of the fact that Obama was not yet in the Senate and didn’t face the same test. But Obama was in public life, saw the danger of the invasion and the consequences of occupation, and he said so. He was right.

Obama demonstrates as well that he is open-eyed about the terrorist threat posed to the nation, and would not shrink from military action where it is warranted. He does not oppose all wars, he has famously stated, but rather “dumb wars.” He also has the edge in economic policy, less because of particular planks in his platform than because of his understanding that some liberal orthodoxies developed during the last 40 years have been overtaken by history. He offers leadership on education, technology policy and environmental protection unfettered by the positions of previous administrations.

By contrast, Clinton’s return to the White House that she occupied for eight years as first lady would resurrect some of the triumph and argument of that era. Yes, Bill Clinton’s presidency was a period of growth and opportunity, and Democrats are justly nostalgic for it. But it also was a time of withering political fire, as the former president’s recent comments on the campaign trail reminded the nation. Hillary Clinton’s election also would drag into a third decade the post-Reagan political duel between two families, the Bushes and the Clintons. Obama is correct: It is time to turn the page.

An Obama presidency would present, as a distinctly American face, a man of African descent, born in the nation’s youngest state, with a childhood spent partly inAsia, among Muslims. No public relations campaign could do more than Obama’s mere presence in the White House to defuse anti-American passion around the world, nor could any political experience surpass Obama’s life story in preparing a president to understand the American character. His candidacy offers Democrats the best hope of leading America into the future, and gives Californians the opportunity to cast their most exciting and consequential ballot in a generation.

In the language of metaphor, Clinton is an essay, solid and reasoned; Obama is a poem, lyric and filled with possibility. Clinton would be a valuable and competent executive, but Obama matches her in substance and adds something that the nation has been missing far too long — a sense of aspiration.