I've been waking up at 4am every day, worried about whether I'm doing all I can to help Barack Obama to pull off the biggest upset of the US presidential primaries.

A win in my home state of Texas on Tuesday would almost certainly clinch the Democratic nomination for Senator Obama. And while history makes Texas an unlikely place to crown an African-American politician, I think it can happen.

Six years ago, I ran for the US Senate, hoping to become the first African-American to win statewide at the top of the ticket. I didn't pull that off. But what I know about Texas from my long political career here - and what I've seen out on the stump with Senator Obama - makes me think he can. The latest polls agree, giving him a narrow edge over Hillary Clinton.

Campaigning in Texas is like running in seven different primaries at one time. But across the state, Democrats are energised. President George W. Bush, our former Governor, is not the uniter we knew, and we're ready for a change. And an Obama victory would be a clear sign that Texas - and the rest of the country - has moved beyond the racial politics that long divided us.

In some ways it is only fitting that Texas be the state to break this important racial barrier. It was the Texan Lyndon Johnson, the master politician, who engineered the passage of the Civil Rights Act of 1964 - and, as he put down the pen he used to sign it into law, told an aide that Democrats had “lost the South for a generation”.

Unfortunately, Johnson was right about my party's troubles in the South. But he was also right that those hard times would come to an end, that we would reach a point where we could put our racial and ethnic divisions past us, and move on, building a diverse coalition like Mr Obama has.

Don't get me wrong. As my old campaign manager always used to remind me, the other side gets to campaign too. After 11 straight losses, Senator Clinton's campaign has stuck a flag in the ground and declared that Obama's streak will end here (and, they hope, in Ohio, which also votes on Tuesday).

But Mr Obama has a kind of energy I've never seen before in a politician. I witnessed it a year ago when, just days after this first-term senator from Illinois announced his presidential bid, 20,000 turned up in an Austin park on a rainy afternoon to cheer him on. (The Obama campaign, which originally planned to hold the rally in a university gymnasium, looks back on that crowd as an early sign of what has been his phenomenal star power.) And I see it now in the faces - young and old, dark and light, liberal and conservative - who have been turned off by partisan politics and are embracing his message of change.

I saw the same possibility in 1995, when I became the first black mayor of Dallas. I had a vision for the city: better jobs, safer streets, cleaner parks, stronger schools. There wasn't anything black or white about it. It was a vision we could all share.

I saw that opportunity when I ran for the Senate. As I travelled across Texas, I talked about how I had governed in Dallas, building coalitions and including people of all faiths and ethnicities. I campaigned hard in the Rio Grande Valley, along the US-Mexico border. And despite all the talk about a so-called black/brown divide, I took a majority of the Hispanic vote, beat a Hispanic Democrat and claimed the Democratic nomination. (Sadly, I didn't manage to beat the Republican John Cornyn, a protégé of Karl Rove, the architect of President Bush's campaigns.)

On Tuesday, Hispanics could make up as much as 40 per cent of Democratic primary voters, their influence felt far beyond the valley. Well aware that they could be decisive, both candidates are running Spanish-language radio and television advertisements. It's true that Mrs Clinton drew strong support from Hispanics in some early primaries. But Mr Obama has been making inroads among them. He beat Clinton among Hispanics in Maryland and Virginia - a turning point in the race in which he also drew support from the white men and working-class voters who had been her biggest backers. In Texas, I see him drawing support from young Spanish-speakers, particularly those who went to college, and those who haven't been involved in politics before.

Senator Obama isn't ignoring the important African-American leaders such as Jesse Jackson who went before him. But he is seeing what I saw, that post-partisan politics is possible if you are willing to reach out, build coalitions and appeal to all kinds of voters - give them the confidence to look beyond their traditions, and sometimes their fears, and go with you.

President Johnson told us this day would come, and when I watch Mr Obama's campaign success, I believe we really are almost there.

Ron Kirk was Mayor of Dallas from 1995 to 2002

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