Trouble sorting database in nodejs and mongodb

I'm having trouble sorting my database from last to first. This is what I have:

Index.js

var express = require('express');
var router = express.Router();
var mongo = require("mongodb");
var db = require("monk")("localhost/nodeblog");

router.get('/', function(req, res, next) {
  var db = req.db;
  var posts = db.get('posts');

  posts.find({},{}, function(err, posts){
    res.render("index", {posts: posts})
  }).sort({_id: -1}).exec(function(err, docs){
    if(err) throw err
    console.log(docs)
  })

}); 

Index.ejs

<% include ./layout/header %>

<% posts.sort({$natural:-1}).forEach(function(x) { %>
    <h1 class="ui header"><a href="/post/show/<%= x._id %>"><%= x.title %></a>
    <div class="sub header">Posted in <%= x.categories %> by <%=x.author%> on <%= moment(x.date).format("MM-DD-YYYY")%></div>
</h1>
<h4 clas="ui header">
<%= x.body %>
</h4>
<div class="ui teal button"><a href="/post/show/<%= x._id %>"> Read More </a></div>

But I get an error!

Thank you for your help.

via jomeco1