Python: How can I setup a loop with a function and a Tkinter GUI?

I wanted to test out a few things in Python and write a script in which you can log in with your name and password. I have setup a GUI using Tkinter in which you are asked to enter your name and password and I have a function (login_check()) that tests if your password is correct but I don't know how to constantly run login_check() while displaying the GUI (root). That's my code so far:

from Tkinter import *

def login_check():
name = entry_name.get()
password = entry_password.get()
if name == "Marvin":
    if password == "123":
        print("You are now logged in")
    else:
        print("wrong password.")
else:
    print("This username does not exist.")


root = Tk()

label_name = Label(root, text="Name")
label_password = Label(root, text="Password")
entry_name = Entry(root)
entry_password = Entry(root)

label_name.grid(row=0, sticky=E)
label_password.grid(row=1, sticky=E)
entry_name.grid(row=0, column=1)
entry_password.grid(row=1, column=1)


login_check()
root.mainloop()