Joe Biden is going to have it tough sharing a stage with Elizabeth Warren. But this is how he could defeat her

Joe Biden remains a strong frontrunner in the 2020 Democratic primary race. In two weeks, however, he will face off in a debate where he will share the stage with all of the top contenders.

Biden's lead in the RealClearPolitics polling average shows he's up nearly 12 points over his closest rival, Bernie Sanders. Elizabeth Warren is just behind Sanders, with Kamala Harris and Pete Buttigieg a distant fourth and fifth. No other candidate is averaging higher than 2.5 per cent.

New debate rules have limited participants to only 10 when the previous two debates had 20 candidates spread out over two nights. It was 2012 the last time Biden was on a debate stage before the first Democratic debate, and it showed. He was not ready for Kamala Harris's attack on him about busing policies. Biden was better in the second debate but got an assist from Tulsi Gabbard when she tore into Harris's record as a prosecutor and attorney general in California.

One other person was missing from the stage when Biden appeared in the last two debates: Elizabeth Warren.

While she still lags a bit behind Sanders in the polls, she's drawing large crowds to her events. While crowd size isn't necessarily a predictor of political success, it certainly can gauge enthusiasm. Warren recently tallied crowds of 12,000 in Minnesota and 15,000 in Seattle.

Warren made strides throughout the summer, releasing detailed policy proposals that include a wealth tax, a $100 billion plan to combat the opioid epidemic, and a proposal to erase student loan debt. Her ideas are bold and don't rely on broad strokes. Her plans are very detailed and her vibrancy provides a strong contrast to Biden and Sanders – despite Warren herself having turned 70 in June.

She also represents a distinct shift to the left for the Democratic Party that aligns with the vision of Bernie Sanders. And that's where Joe Biden is most vulnerable.

Biden represents two eras. One, a bygone era of the 70s and 80s when many Democrats of the time were indistinguishable from many Republicans today. Democrats as a whole embraced the "tough on crime" mentality, a formidable foreign policy outlook, and enforcing rules against illegal immigration. They also largely rejected the idea that the federal government was the magic elixir that could cure all of the nation's ills.

Biden also represents the era of the Obama administration. Perhaps for that, the former vice-president maintains the choice for Democratic African-American primary voters, with 53 per cent support. Sanders is a distant second with 8 per cent.

Warren won't have much space to differentiate herself from Sanders at the debate. So she will likely set her sights on Biden, saying the Democratic Party he yearns for is not doing enough for the American people. Banks have remained a favorite target for Warren's ire. There is little doubt she will go after Biden's cozy relationships with banks and his work on getting the 2005 Bankruptcy Abuse Prevention and Consumer Protection Act passed. That law made it more difficult for consumers to file for bankruptcy.

For Biden to have success against Warren, he must go after her from the right. He must make a convincing case that Warren plans to fund many of her ideas with her wealth tax, one that some experts say is unconstitutional. Biden should also go after Warren's trade plan. What she proposed comes with preconditions that would prevent the United States from entering into a trade agreement with Germany, one of our top allies.

More importantly, Biden must provide a robust defense of Obamacare. He has only offered a tepid defense thus far, and should study John Delaney's criticisms of what it will do to hospitals across the country. Warren is a facts-and-figures person, and Biden will have to show that repealing and replacing Obamacare with Medicare-for-All is unnecessary.

There's still a long way to go. But Joe Biden cannot rest on his laurels and think his big lead will remain in place. Kamala Harris and Pete Buttigieg shot up quickly early on, but have faded fast. Bernie Sanders electrified Democratic primary voters in 2016 but he's almost been invisible during the last few debates, and unexpectedly so.

Warren is hungry and she's going to bring her best in the next debate. If Biden is not ready for her, it could be a long night.