I have traditional ira with $18,000 basis. That is, taxes have already been paid. I took RMD of $7000. IS that $7000 taxable since taxes have already been paid?

Your distribution is partly nontaxable, but mostly taxable, calculated on Form 8606 Part I.  Given that your RMD was $7,000, I'm guessing that the $18,000 of basis in nondeductible traditional IRA contributions represented about 10% of your balance in traditional IRAs.  If so, 10% ($700) of the distribution will be nontaxable and 90% ($6,300) of the distribution will be taxable.  This will also result in your basis carried forward to 2018 being reduced to $17,300.

Thank you. This is the first answer to any question that has actually been helpful.