An advertisement that was published by the Sanders campaign showing former President Barack Obama, praising the Vermont senator, received backlash from Obama’s Vice President and now Bernie’s main rival for the Democratic party nomination, Joe Biden. The advertisement features former President Barack Obama as he extols the virtues of the Vermont Senator.

“Bernie is somebody who has the virtue of saying exactly what he believes, great authenticity, great passion and is fearless. Bernie served on the Veterans’ Affairs Committee and got bills done,” Obama said in the ad.

He continued to say, “I think people are ready for a call to action. They want honest leadership, someone who cares about them, they want somebody who’s going to fight for them and they will find that in Bernie.”

The end of the ad had Obama repeating the cheesy tagline for Sanders’campaign, “That’s right, feel the ‘Bern.’”

The advertisement didn’t sit well with Obama’s former VP. The Biden campaign released a statement saying that the ad was not effective and went on to highlight Biden’s “achievements” during the Obama administration. They claimed that Biden was entrusted with handling the stimulus which saved the country from the financial crisis and for getting the Affordable Care Act passed. They went on to remind people that Sanders almost launched a primary challenge against Obama. Biden has been citing reports that Sanders did try to challenge Obama in 2012 but was only dissuaded from doing so by the then-Senate Majority Leader Harry Reid.

The ad was clearly aimed at targeting a clear sore point for Biden’s campaign, the lack of endorsement from his former running mate, which has some people wondering if Obama would ever give Biden his endorsement.

Some analysts believe that Obama withholding his endorsement is a deliberate move. Since there was no clear leader for the longest time during the campaign for the Democratic nomination, him backing Bernie or any other candidate might isolate the supporters of other candidates who could end up getting alienated. It is likely that Obama is waiting for the winner of the Democratic nomination before he gives his endorsement, which can become a key tool in uniting the different factions of the party, which will be needed once the divisive run for the nomination is over.

That has not stopped the speculation that Obama is unwilling to back his former VP for various reasons. Some cite his “problematic” history of acting strangely with children right in front of cameras as a major weak point which can be exploited should he become the Democratic nominee. More recently, his public speaking gaffes are showing signs that he might not be up to the task of being a presidential candidate, let alone being a President of the United States, which is why Obama might be having second and even triple thoughts about backing him up.