Liberals, Obama and Democrats are counting on Clinton to come through for them. Counting on him to up Obama's popularity. Increase his dwindling approval ratings and decrease his high disapproval ratings.
What Clinton will say or how he says it shouldn't be their main concern. Bill Clinton will come through for them. He will say the right things, he will give the right message. He will not only do it, he will do it well and with the legendary Clinton charm.
What should concern them is that those old enough to remember the Bill Clinton Presidency will compare Clinton's success and contrast it with Obama's utter failure.
Compare:
Bill Clinton had to work with a House of Representatives and Senate that was completely controlled by Republicans by 1994 and still managed to produce the first federal budget surpluses since 1969, for fiscal years 1998, 1999, 2000, and 2001, leading to a decrease in the public debt.
Contrast:
Barack Obama had his first two years in office with a Democratically controlled House and Senate and passed a stimulus bill that did not stimulate, the economy is still struggling and the national debt under Obama increased more in three years and two months in office than it did during 8 years of the George W. Bush presidency. (Source- CBS News, March 2012)
Compare:
Bill Clinton passed welfare reform in Personal Responsibility and Work Opportunity Act which ended Aid to Families with Dependent Children and reduced the number of welfare programs and Clinton did so with support from both political parties. This was Clinton's signature achievement.
In 2003 an analysis was done and that bill was credited with a substantial drop in overall poverty, child poverty, severe poverty, welfare dependence, and an increase in employment, among other things. (Source- Heritage - Charts at that link)
Contrast:
Dependency Index Surges 23% Under President Obama
Food stamp use rises 100% under Obama
Then in mid-July the Obama Department of Health and Human Services (HHS) released an official policy directive rewriting the welfare reform law of 1996. Obama changed the work requirement of Clinton's signature legislation.
Compare:
Democrat Bill Clinton was president the last time the federal budget was balanced, and Republicans controlled Congress.(Source- CNN Fact Check: The Last President To Balance The Budget,” CNN, 2/3/10)
Contrast:
Obama's budget projects that the deficit for the current year will total $1.33 trillion, the fourth straight year of deficits over $1 trillion. (Source- Associated Press, "Highlights of Obama's $3.8 trillion budget" February 2012)
Compare:
Under the Clinton Administration, median household income increased by $6,200 (Source- Statement from Senator Obama on the Census Income, Health Insurance and Poverty Numbers, August 26, 2008)
Contrast:
Real median household income in March decreased by $4,300 since Obama took office in January 2009. (Source- Bloomberg, April 2012)
Compare:
Clinton campaigned on the economy and had remarkable success. GDP growth during his eight years averaged 3.5% per year. (Source- Forbes, July 2004)
Contrast:
Under Obama, America’s 2012 First Quarter GDP Growth Was A “Tepid” 1.9%, Which Was “Too Weak To Lower The Unemployment Rat. (Source- USA Today- June 2012)
In summary, Bill Clinton worked with a Congress completely controlled by the opposite party, Republicans, while Barack Obama spent his first two years in office with a Congress completely controlled by his own party. Clinton outperformed Obama, despite that handicap, in every single measure of success, from economic growth to lowering unemployment, to balancing the budget to cutting spending and public debt, lowering welfare rolls and decreasing poverty levels, etc...
Democrats shouldn't be worried about what Bill Clinton will say, they should be terrified that those old enough to remember the Clinton presidency will compare what Clinton did with what Obama didn't do. Contrast what Clinton was capable of with Obama's performance showing only what he has been incapable of.
(Disclaimer- As I have said before, I voted for Bill Clinton back before extremists took over the Democratic party and I grew up and became a Republican)