Can I make a loan from my trust to a beneficiary?

Yes, as long as you provide for this power explicitly in your trust. You may make a loan, which the beneficiary must pay back with interest. You may allow the beneficiary to repay the loan with money the beneficiary would receive from the trust.

In a similar vein, you can make it clear in the trust that the trustee can make payments for a beneficiary's benefit (e.g. college tuition for a child).