Barclays says a 'trifecta' of factors will lift the S&P 500 to 4,000 next year

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Three major catalysts should help the S&P 500 gain another 12% by the end of 2021, according to Barclays.

The investment firm set its end-of-2021 target for the broad market index at 4,000, which is 11.8% above where the S&P 500 closed on Monday.