PHILADELPHIA — President Joe Biden will hold a fundraiser with Democratic Senate candidate John Fetterman in Philadelphia next week to boost his campaign in a tight and closely watched Senate race that could determine control of the chamber. The Oct. 20 fundraiser in Philadelphia comes days after Senate fundraising reports are due in a race that has tightened with just four and a half weeks to go. Biden hasn’t done much public campaigning for midterm candidates but has hosted several fundraisers to bring in money for Democrats who he hopes can mount a challenge from Republicans for control of …