One of the reasons that centrist Democrats were desperate to nominate Joe Biden and even more desperate to avoid nominating Bernie Sanders or Elizabeth Warren this year was to secure the support of alienated Republicans. The Lincoln Project, the Never Trumpers and a good number of MSNBC hosts are key parts of that group, and Democrats believed that progressives would have no choice but to support the Democratic nominee while the anti-Trump Republicans might be scared off by a progressive nominee.
Whether or not that strategy was wise, the former Republicans are now part of the Biden coalition and they are going to expect a seat at the table. Many of these people are refugees from the George W. Bush administration and have a keen interest in an area they can have the most impact: foreign policy. I explore at Responsible Statecraft.