WASHINGTON/NEW YORK (Reuters) – The largest U.S. auto union and onetime Democratic presidential candidate Senator Bernie Sanders clashed Monday ahead of what is billed as this month’s planned celebration of party unity to defeat President Donald Trump in the November elections.

United Auto Workers (UAW) President Rory Gamble and Sanders sparred on Monday in a phone call over the senator’s plan to have a former autoworker union leader nominate him for president at the Democratic National Convention (DNC), people briefed on the matter told Reuters.

Democrats for months have been carefully crafting a made-for-television pageant to make their case in front of millions on national television for former Vice President Joe Biden to be elected.

Biden, a relative centrist in his party, is attempting to project a unified front after a divisive year-long primary that pitted liberals like Sanders against moderates. Big labor unions – including the 400,000-member UAW – are essential to Democrats, offering organizing support on which the party has come to depend in elections, but many rank-and-file members also support Trump.

Sanders, a Vermont independent who won nearly 1,100 delegates in the Democratic presidential race compared to nearly 2,700 for Biden, had planned to have former UAW President Bob King introduce him for president from a union hall, the people said.

Of course this only happens for Bernie Sanders if the Democrats manage to gain four seats in the Senate – a tall task even if 2020 is another blue wave. The best shot at flipping the Senate is if Joe Biden wins by a large margin and carries the Senate with him. By getting behind Biden and unifying the party now, instead of waiting until the convention, Bernie may be able to help Biden run up the score. If Bernie gets just happens to land the committee chairmanship he’s always wanted in the process, more power to him.