The same-sex marriage debate in the U.S. continues to heat up and will be a level higher with the Supreme Court hearing arguments on Tuesday on the challenge to California's ban on gay marriages and Proposition 8 raised by lesbian couple Kris Perry and Sandy Stier.

To make the debate livelier, Virginia Democrat Mark Warner and Starbucks Chief Executive Officer Howard Schultz added their voices to the growing support for same-sex marriage.

Ahead of the Supreme Court decision, Time says that while it is difficult to predict the court's ruling, there are indicators of some kind of victory in favour of marriage equality. The magazine pointed to Justice Anthony Kennedy as the one likely casting the deciding vote.

It noted the sharp partisan divided in the Supreme Court, which is tackling the issue of gay marriages for the first time, with four justices identified with the liberal bloc known to have sympathy for gay unions and the other four conservative bloc likely to be hostile to the idea.

Mr Kennedy, known for his swing vote, is a supporter of gay rights, having penned the majority opinion in Romer v Evans case that struck down a Colorado amendment that stopped localities from passing legislation protecting gays from discrimination and the landmark Lawrence v Texas decision that struck the state's law against gay sex.

Time opined that the inclination of Mr Kennedy to protect gay rights could possibly be because of his being a California establishment Republic who has met a lot of gay people. The magazine cited a new PewResearch study that the biggest contributory factor for people to change their attitude toward gay marriage is knowing a gay person.

One politician who acknowledged an evolution on his views about gay unions is Mr Warner who had said in a statement that supporting gay marriages is "fair and the right thing to do."

Mr Warner is the first Virginia governor to extend anti-discrimination protection to LGVT state workers, supported in 2010 the military's Don't Ask, Don't Tell policy, and signed in early March an amicus brief seeking the repeal of DOMA.

He is the fourth national politician who had changed this minds about gay marriages this month. The three others are former Secretary of State Hillary Clinton, Ohio Republican Senator Rob Portman and Missouri Senator Claire McCaskill.

Mr Schultz, CEO of the world's largest coffee chain, told a Starbucks shareholder that he could sell his stocks if he disagreed with the company's stand on same-sex marriage which the latter warned is affecting Starbuck's share prices.

When Starbucks openly supported in 2012 the Washington referendum that legalized gay unions, the National Organisation for Marriage pushed for a boycott of the popular coffee chain.

Shareholder Tom Strobhar pointed out at last week's shareholder meeting that the chain's sales and earnings were a little disappointing which he attributed to the boycott.

"If you feel, respectfully, that you can get a higher return than the 38 per cent you got last year, it's a free country. You can sell your shares of Starbucks and buy shares in another company," Mr Schultz replied amid the shareholders' applause.

He stressed that the decision to support same-sex marriage was not an economic one but because of Starbucks decision to embrace diversity since it employs over 200,000 people who also have different sexual preferences.

The Wall Street Journal listed four possible scenarios of the Supreme Court ruling on the challenge. These are a split decision, a limited ruling on Proposition 8, a ruling on standing and a surprise.

Under the first scenario, one likely result would be the justices ruling that California voters are entitled to ban gay marriages if they wished or a straight-up split decision which would lead to more heated same-sex battles on the state level.

The second scenario could be seen as a triumph for pro gay marriage groups, but at the same time would allow states that never allowed gay unions to continue their policy.

As to the fourth scenario, the WSJ noted that chances for a surprise decision are doubled given Chief Justice Roberts's vote in 2012 to uphold the health law's insurance mandate.