Genesis 14:17-20 (NJPS):
When he returned from defeating Chedorlaomer and the kings with him, the king of Sodom came out to meet him in the Valley of Shaveh, which is the Valley of the King. And King Melchizedek of Salem brought out bread and wine; he was a priest of God Most High. He blessed him, saying,
“Blessed be Abram of God Most High, Creator of heaven and earth. And blessed be God Most High, Who has delivered your foes into your hand.”
And [Abram] gave him a tenth of everything.
Several things about this story make me suspicious that it might be intended as metaphorical:
Melchizedek doesn't show up at anywhere else in the Torah and only once again in Psalm 110 (maybe).
His name (Malkiy-Tsedeq <04442>) is composed of two words: melek <04428> meaning "king" and tsedeq <06664> meaning "righteousness" or "justice". (The NJPS of the word in Psalm 110 is "a rightful king", which is why that reference is only a "maybe".)
Abram pays this man a high honor by giving him "a tenth of everything," but there's no explicit reason given.
He is king of Shalem <08004>, which is the same as shalem <08003> meaning "complete, safe, peaceful, perfect, whole, full, at peace" and derived from shalam <07999> meaning "to be in a covenant of peace, be at peace".
Given that this enigmatic character with associations to justice and peace appears right after a conflict between Abram and the four kings, does the text encourage us to interpret Melchizedek as metaphor?